Shifting into gear or braking to a stop causes engine to die.

So driving my truck yesterday I noticed whenever I would brake the truck would kind of work against the brakes and the rpms would jump as I came to a stop. This eventually got so bad that the rpms would dip too low and the engine would die, almost as if the speed was directly correlating with the rpms rather than staying at idle level (~700) when braking to a stop or being entirely stopped while still in gear. The rpms would drop to maybe 400 or 500 then jump to maybe 1300 and then the engine would die. To account for this I would throw it in neutral while coming to a stop and then never actually stop moving, just roll through the stop sign and throw it back into gear halfway through the intersection. I wanted to check if maybe the transmission fluid was low so tried to put the parking brake on and put it into gear and this continued to happen as with the normal brakes except even worse, the rpms would jump between 500 and 1500 about once a second until I took it back out of gear into park or neutral. Im completely confused by this but from what I’ve found online sounds like a Vac leak somewhere or something to do with stuff that controls my Idle Air intake and thus rpms. Thanks!

(2000 4x2 Triton 4.6L XLT Standard Cab)