what happened to my transmission???

[92SAS]

1992 K1500 SAS 60/14 combo 4.88 gears 315/75/16 BFG MTs. 700r4.
I drove my truck last week end, no wheeling, just running errands for which I needed a truck,(DD is a Honda civic 31 MPG).
I put the truck in the garage. During the week I put a set of 52 inch springs up front
and longer shackles in the back all in a quest for flex and soft ride. I installed a cb and antenna.
This weekend I went to test out my new springs and what do you know my truck would not shift out of first gear??? Reverse is good, drive (1st is good,no slipping).
It makes no unusual noise has plenty of power(in first).
I dropped the pan to check things out (I'm no transmission guy) there were no shavings,objects or broken pieces, just the usual fine black clutch stuff on the magnet. The fluid was bright red and had no burned smell. I just changed fluid and filter a year ago! I don't use any additives except for 1oz per quart of Lube Guard (the red bottle) I have never had even a hint of problem.
I checked the governor and the little green gear on the end and It looked ok? but I wouldn't know what to look for. And the TV cable is adjusted properly.

Does anyone have any idea of what happened and how to deal with it??
Any help would be greatly appreciated

 

[Solid94]

When you changed the fluid did you do it yourself or have someone else do it? Because if you did it your self you might want to try adding the gm friction additive that the tranny needs. When I changed all my fluids my shop told mento add this additive they gave me in the tranny. And a different one in the axel

 

[NAST96]

I didnt know you had to use a special additive when dropping the pan and changing fluid. Is this only for the 700R4?

 

[JonZ71]

you don't need special additive unless owner manual states you do. dextron 5 or 6 is what you should use, and it sounds like a VSS problem or servo, but idk if 700r's ave vss's