C6 Slipping??

[ah1988ford]

My c6 trans seems to be slipping. The truck will rev up really high (redline) and it wont shift unless you use the gas pedal almost like a clutch. I can shift it by taking it up to about 2500-3000rpm, give it a bit of gas let off of the gas then give it some gas and then it will shift. This is very sporadic some times it will shift without having to let off of the gas and then hammering it, other times I have to do the gas pedal thing. This just recently started to happen after I had my booster replaced, so does this sound like a vaccume issue ?? It has never really shifted right, so I dont know if its a sign the tranny is going our what??
The first thing I checked was the fluid and the fluid is pretty new and the trans if full.
I will try to get a vid tomorrow, its hard to explain.

EDIT: I forgot to mention when I put it in reverse the truck goes but really slow, but when I get around 1800rpm there is a big "clunk" and it feels like a really hard shift and it feels like something wasnt engaging and then it engaged?

 

[OLDBULL8]

There is a short piece of hose from a steel line to the tranny, see mif that is disconnected or cracked. There is a VRV on the IP, it has two vacuum hoses on it, make sure there connected. Check all your vacuum lines, since the trouble started after the brake vacuum was changed.

 

[fordf350man]

you might just have to adjust the vacuum modulator on the back of the transmission, mine did the same thing, i just replaced it with a black stripe factory set new one and it took care of it, still shifts ard but i was told it has a shift kit, cant confirm but everything works fine so i assume it does

 

[ah1988ford]

Ok thanks guys, ill play with the vrv and check all of the rubber.