Chevy Tahoe P1870 Transmission Slipping

Problem with my 1998 Chevy Tahoe codes = p1870 Checked the code "trans slipping". Checked fluid, full, and clean (red). I believe the fluid psi solenoid is bad. Normally the vehicle runs fine. Then when put under a load or driven hard (highway).
The light comes on and the trans shifts funny. When the trans acts up, the 1-2 shift is very harsh, and a burning smell is present. Upon sitting parked for around 1 hour, the trans is fine until you apply torque to it again. I will be changing the filter tomorrow, but would like your opinion.

Answer: P1870-component slipping, can be caused by a problem in the valve body, but with that many miles on it, it may just be time to overhaul because of slipping components, The condition of the fluid-if burnt, means trans. needs to come apart and look for a failure. Again, with that many miles, probably just worn out. Try the filter and fluid change to see if it helps. Th hard shifts are most likely caused by the line pressure being raised to compensate for a slipping component.

Question: I have the same problem but trans was serviced valve body replace torque converter replaced and it still does the same thing problem may be a restriction in the trans cooling line and radiator may want to have some body do a pressure test.
 Answer: While this problem occurs, does the trans leak fluid?

Short cut. Don't remove P/S pump, instead remove all the water pump bolts you can (7 of them) then loosen the last one behind the P/S pulley get a crow bar and break the water pump off. This will break the ear and the pump will slide out. On the new part cut the ear into a slot with a cut off wheel and the new pump will slide back into place without ever removeing the eighth bolt.