So i got my 1998 Tahoe with the 4L60E transmission and the autotrac trannfer case (junk).
i am having some issues.
My transmission shift really hard especially from first to second, sometimes has a hard time downshifting to the right gear under hard excelleration, and when cruising around 45 to 55 it feels like the torque converter is constantly locking in and out.
The problems also are sporadic, sometimes it runs fine, sometimes the symptoms are pretty rough.

Is my transmission tottaly smoked?
If so, anyone know how hard a rebuild to do on my own would be?

I will hopefully be pulling it apart sometime soon anyways to swap the autotrac for a normal part-time case.

Most likely the valve body has a worn valve bore for the converter clutch regulator valve.

The firm shifts are because the trans is in a failsafe mode that maximizes line pressure, check engine light on?, if so most likely a code of p1870 (trans component slipping).

The cheapest way to fix is to pin the valve with a heavy spring, basically eliminating the soft regulated apply of the converter. You may notice a firmer apply of the converter clutch but its not uncomfortable.

The way to fix it and retain the regulated apply of the converter is to replace the valve body or fix it with a Sonnax valve repair kit.

http://www.sonnax.com/part_summary.php?id=3578&pl=3

What JK said but may be easier to exchange yer old valve body here:

http://www.valvebodyxpress.com/