1995 ford f150 with 4.9 eng. manual trans. Truck starts shacking ,bucking in 3rd and 4th gear when at desired speed truck will smooth out but will start bucking about every 30 seconds .
I had fuel tank cleaned and put in pump truck buck after going to 3rd and 4th
gear . Truck will smooth out when desied speed is reached for about 30
seconds then starts bucking again for 10 to 15 seconds corrects itself and
starts process all over. Any ideas what I might beable to do.
It could be the transmission. It could also need a tune-up. Is the bucking and shaking the result of misfire? Find someone with an engine analyzer and see if there is a miss.(s). Normally if there is a miss in a couple of cylinders it shows up under load. Process of elimination. Check the easy things first.
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