clutching, but no clutch?????????????

[RROSIN1]

i have an 83' 300D. it sat for a couple weeks while i fixed a fuel line that was leaking(no big hurry). now when i get above 2200 rpm it starts to learch like it has a clutch engaging and dis-engaging. it does it on hard acceleration or easy. i'm guessing a vaccuum leak but dont know where to start looking(may be wrong all together). oddly, my 86' 300sdl has started doing the same thing, plus loses power going up a hill, to a crawl. and it wont shift out of overdrive unless you let off the fuel???
thank you for any and all assistance