rough shifting

All of a sudden my 1986 F-150 302 auto started shifting really rough. It has always been smooth as silk in the 26 years and 200K I've had it. Now I have to rev it really high and wait for it to upshift. I used to be able to accelerate gently, and just burp the gas and it would shift. I thought it might be a vacuum leak some where, but can't find it. Any ideas would be greatly appreciated.

200k at 10 mpg thru a truck that was $5800 off the lot!!

I would assume the vacuum leak also.
I would suspect the vacuum hose on the modulator diaphram is the culprit.

Thanks for the reply Tony. Can you point me towards this diaphram thingy? Not sure how the vacuum is connected to the tranny.