C4 Trans not shifting when Cold
So I got my car back a few days ago from the shop for an engine repair and I noticed some issues with my c4. When cold, it doesn't want to upshift when in Drive. It does go in reverse and 1-2 are fine when shifting manually, but when I go into drive it over revs, or seems like it goes back to 1st.
When the car is all warmed up the car can shift through all 3 gears, the shift points are much wider now as I assume they adjusted the shift points but the shop owner is saying they didn't touch anything.
When Cold, I check the fluid level and it shows little to no fluid, when warm the fluid is at level.
the thing shifted Great before I dropped it off though I did have a 2-1 down shift "Clunk", I spoke with the owner of the shop to look into this.
I checked vacuum pressure on the modulator, and I am getting pressure. Any suggestions? could it be incorrect fluid? or stuck relief valve? Its push-in modulator and the c4 was built by Performance automatic a few years back its the super streeter from PA Automatic.
****update so I spoke with the mechanic that worked on my car, he did adjust the shift points and added some fluid. Before I send the car back I would like some suggestions as I would like to look into this myself. before handing it off to them.