i am having trouble finding a vacum leak? 88 2wd 350 1/2 ton. tbi

i recently swapped burned up th400 with a th350, after took truck out for a drive, seemed to run and shift fine on a 25 mile trip. later that day went for another drive and engine stalled at stop sign, started but had to keep revs up or engine would stall. once got home it will start but will not stay at a smooth idle, surges then dies if put in gear or let of gas. I replaced egr valve, but no luck. also checked gas seems to be flowing out of injectors okay, i also changed fuel pump,fuel pump relay, and fuel filter recently. i tried a trick was told about and sprayed wd40 on throttle body and the engine ran very smooth until wd40 burned up, im not for sure but i think this could be a sign of vacum leak, i have checked all hoses, most of which i replaced when swapped transmissions. could i have possible routed something wrong, or am i going in wrong direction with vacum leak? any help would be great.