Is my Trans slipping



1987 GN 35,000miles,B&M trans cooler with a 6"Spal blowing across it all the time,stock trans with Type F fluid and 1 extra Quart of fluid.OAT =65°

In OD while driving and then getting on it(pedal mashed to floor),I see the boost gauge jump to 20psi in a milli second ,so I get out of it and put it in D and problem did not show itself again.

I guess I need to know if the boost will jump ski high if the trans slips ,almost felt like I hit an oil spot without the fishtail that you would get..

Mods are

TE61 21-22 psi
009 inj
PTE front mount
translator +
SMC Alki
Oh also 9" percision LU 3200
Thanks for all the help