Hard shifting i have a 1991 gmc sierra single cab, it shifts hard on 2nd gear only. It seems like it just takes long to go into gear!

You have the electronic version of the 4L60, so if it was doing it before with your old tranny. I'm going to point the finger at the computer. Probably nothing wrong with your old unit.
If you didn't replace this, then maybe you should.
https://www.carparts.com/details/GMC/C1500/AC_Delco/Automatic_Transmission_Wiring_Harness/1993/Sierra/8_Cyl_5-dot-0L/AC24241212.html

Not a wire. Your transmission shift cable may be disconnected from the throttle. Or if you have a vacuum modulator the vacuum tube may be disconnected. Check your fluid level.

clutch is shot

Solenoids inside the transmission or the control module.

That could be a perfect reason to take it back to the shop where it was just repaired for repeat service. Either that or you spun out in the mud.

1 Ck A/T fluid level & quality
2 Scan/ck for code(s)
3 With scan tool connected,road test vehicle/Ck parameters....
....time for a pro !!

If you need further help, reach me via phone at https://www.6ya.com/expert/ralph_2f0886b7d6af32ce

Your problem likely resides with the hydraulic valve that operates the band for second gear, or lack of hydraulic pressure in the transmission. If the actuator in the transmission that operates second gear is getting sticky, then it will cause this. A filter change and flush may help, but it's likely time to start looking for someone to tear down your transmission, or replace it.

Your throttle valve on the transmisson is probley not adjusted to spec on this vehicle it runs from carb to right side of trans.


hope this helps

Trans is in safe mode, you will have to get scanned to see codes.