Hey guys, when I accelerate in 1st gear, it goes good, but then you can feel the truck being "held Back", it does not accelerate as fast, RPMS stay the same, it just feels like someone is holding it back or it is pulling something. It does not do it in any other gear, just first. I was thinking vacuum leak?

The truck is a 85 f-150 4 speed manual, 300 I 6.

 

Might wanna see if the parking brake is in any way engaged

 

Wait nvm just read the part where it says it dont do it in any other gear