My 89 Chevy 1500 Silverado jerks when put into gear from park to drive why? More details below plz help?

There are alot of things that can make it jerk or surge. May not be engine problem but problem with trans. Biggest problem I can think of on this truck is vacuum leaking on the tbi gasket. Leaks in the back. Causes alot of problems most of which is surging and high idle. Which is what could cause the harshness when you put it in gear.