92 best..but no go

'92 Sonoma 4x4 SLE 4.3 TBI 700r4 trans and 180Km. Full throttle causes a low frequency ROAR. Cannot get the truck above 30 mph. Any suggestions? My son and I have rebuilt this most excellent machine from the ground up.....much B,S,T. He planed it into a culvert a few days ago and said that there was about a foot of water in the cab. Not enough to get the ECM, but who knows.