Here are ratings from TrailerLife for
1999 Ford Ranger with 4.0 V6 which is the earliest they show:
<span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">Ranger 4.0 V-6 6,000</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">a,c</span></span></span></div>
<div align="left"><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Ranger 4WD 4.0 V-6 5,820</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">a,d</span></span></span></div>
<div align="left"><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Ranger SuperCab 4.0 V-6 5,980</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">a,c</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">Ranger SuperCab 4WD 4.0 V-6 5,660</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">a,d</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">Ranger 4.0 V-6 3,660</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">c,f,i</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">Ranger SuperCab 4.0 V-6 3,520</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">c,f,i</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Ranger SuperCab 4WD 4.0 V-6 3,200</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">d,f,i
<span style="font-size:10pt;line-height:100%">I found this at:
http://www.trailerlife.com/images/do...owingguide.pdf
Here are the codes:
<span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">
<div align="left">a</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Requires automatic transmission and towing package.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">b</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Requires 3.31:1
axle ratio.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">c</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Requires 3.55:1
axle ratio.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">d</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Requires 3.73:1 axle ratio.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">e</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Requires 3.98/4.09/4.10:1 axle ratio.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">f</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Manual transmission.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">g</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Fifth-wheel towing.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%"><div align="left">h</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Automatic transmission.</div>
</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">i</span></span></span><span style="font-size:8pt;line-height:100%"><span style="font-family:Helvetica-Condensed"><span style="font-size:8pt;line-height:100%">Must be equipped with heavy-duty towing package.
<span style="font-size:10pt;line-height:100%">Hope this helps.
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