with the TGPs, the PNP switch is very simple, whenever in neutral or park, a circuit is completed and the pin supplyin power to it should read VERY few volts(less than 1), but in any other position, it breaks the circuit and you should see +12V on that wire.
easy test: disconnect the connector and see if it will get above those revs in any gear. when it'* disconnected, the ECM thinks it'* in drive, and shouldn't limit RPMs until the normal limited kicks in, around 6K.
if that doesn't work out, follow this diagnostic tree.
1995 Monte Carlo LS
3100, 4T60E, OBD1 Conversion...for now, future plans include a 3900, T04E-46 (Knock-Off) turbo, and a F40.