sounds like air or dirt in the lines, or a check valve at the tank.
1) thurn off the gas at the tank.
2)Slowly disconnect the hose from the tank(in case it is pressurized)
3)re-connect the hose to the tank
4) very slowly open the propane
valve on the tank (if it has a built in check valve(high flow preventer)
this will stop it from activating)
5) turn on one burner and light
it, watch it for a few minutes and see if the flame looks ok . if it does,
the others one at a time.
6) if this doesn't work then look for spider webs etc in the burner tubes.
If you have air in the line, it can take a little while to get all your burners to full flame, but not more than 2-3 minutes each