1996 Trans Am with a 4L60E A/T. Problem started to happen on Friday. Saturday did a filter/ fluid change. No metal shavings, and what I would guess is a normal amount of 'grey goop' around the magnet on the bottom of the pan. Problem persists. I've got to get it up to about 2800 RPMs and just under 20 MPH before it is ready to shift, but it will not do so until I let off the gas pedal completely, then step back onto the gas pedal and it'll shift into the next gear. If I do this smoothly it almost feels like there's no problem at all. Once I get it past the initial shift, it accelerates as it should.
I've taken it down to 1 on the shift knob and once it hits the point where it should upshift I throw it into 2. Nothing unless I take my foot off the gas. However, if I keep my foot on the gas and move the knob from 1 to 2, then 2 to 3, then it will shift without having to take my foot off the gas.
Any ideas? Could the 1-2 shift solenoid have gone bad?