OK i have a 91 TII with some few Mods. I was on the Highway when i pushed it a little and all the sudden when my rpms where going higher about 5000 It stop for a sec. Then it started to shake at first i thought it was a tire, but then the engine was shaking pretty bad, My idle is ok about 800. i notice my vac is higher like it had a vacuume leak but i could not find anything and when i give it gas its worse it doesnt die, but not drivable all i did was add a fuel cleaner the day before. any help???

 

A vac leak causes LOW vacuum. Bad seals also cause low vacuum. What vac are you reading?

If you indeed have low vacuum, then your compression is also likely to be low.

Compression test it.

 

do a compression check first

 

i guess i will even though i rebuilt the engine like 3 months ago i really think it could be a fuel problem but idk

 

Compression test, and the fuel cleaner may now just be going through the system. Check the plugs to see if they're all fouled up.