700r4 only shifts P, R, N, and 1st. Will stuck TV valve do this?

[G-NUT]

Looong story but my '83 700r4 worked fine until it didn't. When it didn't, what happened was I was driving my burb pretty easy, it shifted 1, 2, 3, 4 and as soon as it went into 4th it dropped back to 1st. No it shifts beautifully into P, R, N, and 1st. I will not shift into any other gears automatically NOR manually.

When I shift manually from 1st to 2, 3, or D the trans just stays in 1st (low). I've scoured the net for several weeks. I've read in detail the factory service manual and the 1984 GM 700r4 transmission manual.

A while back I installed a new Monster Trans 1800 stall T.Q., new front and rear seals, filter, fluid, and a B&M shift kit in the Heavy Duty option. I'd put about 100 miles on it after doing all that before this occured.

I've verified fluid levels, TV cable adjustment. No go.

Verified the Governor was ok, and it was. But I went ahead and replaced it with one from Monster Transmission. Still no change.

I pulled the valve body back down. Broke it down to a bare casting. Cleaned the V.B and all valves and components. Put it all back together. Same issue.

I've read online about the Throttle Valve sticking being a "known issue", and that there is a modified TV valve for this that TransGo sells as part of their SK700 kit. I'm thinking about getting this and installing it to see if it helps.

Before I buy the TransGo kit, my question on here is whether or not this may fix my issue. Would a sticking TV valve affect the shifting only in automatic mode or both automatic AND when I manually shift through the gears?