This truck came in with problems. When you start it up and drive it (forward or reverse) the transmission hooks up and is strong. As soon as you change directions it looses power. If you shut it off and wait for 5 minutes and restart the truck the transmission will be OK until you change directions again. We changed the solenoids but that didn't fix it. We don't think it is the clutch packs because when it does go into gear it is strong. Pump pressure is 90-120 psi. Forward Pressure is only 40 psi. The valve body shows some wear but we didnt see any major problems. Please Help!