This is in regards to my '95 F250 4x4 but it is the same principle. Anyhow, when my truck goes to shift itself into 2nd and 3rd, sometimes it makes a loud hissing "turbo type" sound with a slight delay into shift. My brother who is more well versed with mechanical details indicated that it is probably a clogged vacuum off the transmission. Question is, does anyone have a pretty good idea where to look to correct this? I am quite handy with cars and usually do my own repairs, but have never screwed with a transmission, and my brother is not a mechanic, so I cannot exactly quote him as 100% correct.

Any ideas?

It is a 5.8l V8 auto 4x4.