I have a 1995 Buick Regal, 3.8 with the 4t60e trans as stated. I was just gifted this car, and have already done a myriad of small things to get it road worthy again after it sat for a few years. Someone please tell me I'm not alone in cursing GM engineers in regards to the oil pan seal job... But I digress.
The car has a weird first gear engagement issue.
The car does this whether warm or cold, and seems odd that a car with only 75k miles on it would have this issue.
-Shifting from Park to Drive: No first gear engagement unless a slight stab of the throttle and it engages on the deceleration. Once moving it clicks through gears perfectly smooth.
-While issue is occurring in drive and not engaging, shifting it to "1" on the gear column will engage the first gear after about 1 and a half seconds.
-While the issue is occurring from a stop in drive: I can shift to neutral, park, or reverse and then back to drive and most of the time it engages first gear.
-When driving in second or third, I can stab the throttle and the trans promptly and smoothly shifts to first.
-When going from any gear other than first to a complete stop, it fails to engage first. If the car never gets out of first gear, it will stay in gear no matter how long i'm stopped.

It was low on fluid due to a leaking trans pan seal, but promptly fixed with a filter change and refilled. Old fluid was so clean I would have drank it, and had no smell. Slight amount of metallic "powder" on the bottom of the pan and on the magnet. Did not seem like an excessive amount and no chunks. The issue persists. Drove about 100 miles, still persists. Added a lucas (without stop-leak) friction additive, still persists.
Its odd to me that putting it in first gear on the column is completely fine, yet the car won't engage it on its own from a stop.
Someone care to chime in? I am planning on selling the car, but in saying that I do have the capability to pull and swap a trans if needed.. even though I really don't want to.
Thanks.
Sidenote: as a college kid who blasts around in miatas, wrx'* and 350z'* all the time.... this thing is a BOAT. I feel like jack sparrow on the highway, and the automatic antenna going up everytime I start the car makes me feel official, lol. So much smooth, so much plush, so little corner ability. Its so much more fun than I thought it was going to be.

My guess: Something is gummed up in the valve body . . . or something leaking. I'd bank on something gummed up.

I'd look at the shift solenoids next. Problem is they're in the side pan.