91 trofeo trans ,slips then thumps into gear

Its been a great car ,but has been sitting for about a year now,I was inspecting the trannie with the pan off and noticed one of the lines was loose ,it had a clip that held it in place and a small hose that junction 2 hard lines ,I replace it with a factory piece that seemed to fit better.I got the car out on the road and it rean beautifully for about a mile then when I came down to a stop the car wouldnt engage into drive,whats up?Is it a bad trans ? Does this seems to be a vacuum problem ,selinoid?

If the fluid is full, pull the pan down again and recheck what you did.