Auto trans diagnosis - falls into 3rd at 60

[greasemonkee]

This auto trans I'm working with on a '97 is above my head. I see ambiguous troubleshooting direction (via factory manual) at this point so maybe someone can give me an idea if the problem is internal -

Recently replaced the TPS, checked the voltages according to the factory manual and all is good. The symptoms are primarily at 60 mph it drops into 3rd regardless of throttle position. Once the lockup engages at 45, the thing will not come out when full throttle is reached. Also, it seems to shift early in the lower gears at full throttle
This tranny has 170k.

Thanks for the help guys.