Tans Selenoid?

[1995z28]

Ok so this is just what im basing my guesses off, but basically my symptoms of the problem that keeps occurring is very poor acceleration (almost dragging), seems to hesitate when its switching gears, hard down shift, and even sometimes (seems to be when its cold out) it stalls!! usually when im dropping below 10 MPH. I have an automatic trans in a 1995 Z28. Please help!!! Also, idk if this helps at all but the shifter is very stiff when switching out of park, and it takes a second or 2 to engage in to the the desired gear. Maybe just linkage? No clue. PLEASE HELP!