Hey- I am new so please forgive any faux pas-After fueling up, suddenly would not upshift, but if moved to neutral after reaching shift point or higher rpm would slip into higher gears upon shifting back into D- your manuals on this subject seem to only cover diesels up to 1985- can you direct me to appropriate manual/technique/parts/etc I am guessing vacuum trouble but know nothing more on subject- thus I would also like a primer on the vacuum system in general-Thanks!