Hard Drive to Park shift

[K20Submarine]

Hey everyone, well I just went from an 88 manual toyota tacoma to a 86 K20 Suburban, its been a long time since Ive driven an automatic, now Ive got the truck sitting waiting for some minor maintenance when I get the money. Now here's one of the issues I want to address, when I shift the truck from Park to Drive I can feel the truck pull pretty hard, and I guess the best way to describe it is that it "bumps" into gear. There's a slightly loud pop and then I can feel the truck pulling if I let off the brake. Now going from a manual 4 banger to this beast is a whole other world so I just want to know if this is normal? Or if there are some things I should check? Thanks guys and Ive got some more questions for later on but this is top of the list right now.