TC lockup problems

[TRAX]

I'm running into an oddity with a friend's car that is becoming increasingly
difficult to troubleshoot.  The car is a 1991 Z-28 305TPI automatic.  This
car has a transplanted 350 (w/ 350 knock sensor), 2400 stall converter, and
3.42 gears.  He is running a custom PROM in the 730 ECM.  The ScanMaster
scan tool that we are using shows that his TC is locking up under WOT at
approximately 82mph.  All TC lock and unlock values in the tables are the
same as the stock 305 tables.  The Lock and Unlock mph contants have been
upped 19mph.

Under WOT we are seeing consistent knock retard of 1-2 degrees at 82mph.
Furthermore, the Engine RPM DECREASES approximately 150rpms even though you
have the throttle nailed.  Under further inspection we determined that the
TC was locking up at exactly that same mph.  This explains the RPM drop and
the slight knock.

What could be causing the TC to lockup??
Could the use of the 305 tables cause this??
Is the PROM the only control for TC lockup?

Tim

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