Ford Repair: 1990 merc., engine vacuum, clutch packs

Question
I have a 1990 Merc. grand Marc. It has a shifting problem between 2nd , third gears. I've read about throttle body, (where is it), and Modulator Valve, Where is That?

Answer
hey, it is located directly on the side of the transmssion and it will have 1 vacuum line going to it from the intake manifold or throotle body.. but if it is faulty i usualy see a long delayed shift from 1st to second then second to 3rd, the modulator detects engine vacuum, and when the engine is at wide open throttle you loose engine vacuum temporarly, this modulator detects that drop of vacuum and downshifts the transmission for more power, (also called kickdown)  this sounds like you may have n internal fault with the transmission, like maby a leaking seal inside on a piston, or even a bad actuator, the only way to check this is to have it pressure tested by a transmission specialist, it may also have a worn set of clutch packs,, If you need t know any more about this operation please follow up.
Chris