chevy S-10 sounds good but takes forever to go on 1994 Ford Thunderbird

we changed from a 2.2 to a 4.3 in a chevy S-10 it sounds good idling but when you go to drive it it takes forever to git up to 50mph or higher what could the problem be?

Asked by for the 1994 Ford Thunderbird
What else was changed besides the engine! Had to change the ECM. What else? What year is this S 10 truck?