Does the transmission have any issues now? The only accumulator you can check is the 1-2 accumulator, 3 bolt housing near where the harness comes into the pan. It may have a plastic piston in it, which are known to crack and cause some apply issues. You can pull the servo out to and upgrade to the corvette servo, which will firm up the 1-2 shift a bit.
Edit: was thinking it was a 4l60e, so it won't have that harness, but the servo will be the same