Gear Selection
Is the transmission slipping in first until it engages second and the slippage ceases?
Have you tried a reset of the tcu to factory specs and observed how that affects shift points and rpm's?
Just some ponderables to ponder

The transmission used in the 1997 - 1999 have issues with certain parts in the valve body. Two parts are directly responsible for the 1 -> 2 shifting: one is a solenoid (that is also for the 4 -> 5 shift) and a valve/spring called "regulating valve overlap 1 -> 2". For up to 1999, another spring (not the one I mentioned) is known to break.
The best thing you can do is to find someone who can scan the EGS (ETC) DTC. There might be a root or stored DTC in there to pin point the problem.
Or if you are going to do a fluid/filter change soon, you can check all these springs one by one to see if any is broken or collapsed. They are very inexpensive.


