TH350 Hitting 3rd at 70MPH!

[texascowboy593]

The truck: 77 K10, 400 powerplant backed by a TH350 with an estimated 60K miles.

I've had this truck (2nd owner) for 3 months now. A couple weeks ago while driving at highway speed, I felt the truck kick down from 3-2 although my speed didn't change. I accelerated and it dropped back to 3. Very strange.

Before this incident, it would shift perfectly in city driving (40-45MPH) thru all the gears and at highway speeds. Now I can't get it to hit 3 unless I race the RPM's up like crazy and hit about 70. The 1-2 shift still hits at about the right point. I do not have a tach yet (budget).

I started with the simple stuff: Checked fluid level/quality. Level good and slightly burnt smell although still crisp red.

I checked vacuum line from direct port on manifold down to modulator. Was worn and flimsy so I changed it out. Checked other vacuum lines throughout system. All good. Changed out modulator for a new redline one.

I pulled the governor to check all moving components, weights, springs and gear. All moved properly including the valve inside and gear was clean with no wear.

My next step will be to change filter/fluid but that will be a couple weeks off. I've done it before but that was like 15 years ago and I'm not a transmission expert by any means.

The only other suspect item that may be a clue for y'all is that ever since I got it, reverse always takes 2-3 seconds to engage after shifting it into reverse.

Any ideas on other things to check? Any clues from this account that smells of impending transmission failure?

Thanks!