1991bird tranny possibly sliping

i have a 1991 t-bird they ust put a new engine in and the tranny seems to slip i think, I press on the gas and it takes a while to go it catches the gears but it takes long to get speed could they have possibly put something wrong? Cuase the tranny ran fine when the motor blew. and all of a sudden the tranny started doing this right when they installed the new motor it also has the oil light on in the dash but im not sure if thats for the engine oil or tranny oil i checked both the fluid levels on the engine and tranny and everything its fine im hoping its something simple. Please help me as i drive this car to work.

sorry i forgot the most important things when its on reverse it goes fast like its supposed to only when i put it in drive that happens. And it also is leaking tranny fluid not sure where from ill check as soon as it starts driping oil again.

never mind lol i had the sme problem the other guy had with the thing loose i connected it back up and now it hauls butt But its still marking it needs oil for some reason maybe the oil just needs to get to the tranny or something . thanks anyway