Kickdown is 3-2, or 2-1. The kickdown doesn't prevent shifting only holds higher line pressures during the increased load.

The valve body is the "brains" of the operation and uses the input from the modulator and governor in accordance with the servo.

Again the kickdown has nothing to do with actual shifting, othewise if you are traveling at 50mph and go full throttle and "kick-down" to 2nd gear, by your logic the transmission will remain in 2nd gear until when? Until you come to a stop and put the trans in Park?

No, eventually, the transmission shifts back into 3rd when the governor, modulator and servo actuate the valve body.

A lot of guys think wiring (there's that word again) the kickdown lever in the engaged position creates higher line pressures in all situations and it doesn't. I fell for it, I tried it and it didn't work. It made no difference. The transmission still shifted perfectly fine.

Josh

 

Not . If the trans starts out held in first , it stays in first ,till governor shift . .....

 

The vacuum modulator controls the shift firmness and the shift timing by modifying the signal from the governor. The throttle lever is used to control downshifts, but also works in conjunction with the governor and vacuum modulator to downshift.
I ran a C6 for years without the throttle lever connected, and the shifts varied and downshifted semi-normally. I had the vacuum line fall off on my van with a C6 and it would shift manually between 1st and 2nd, but wouldn't shift in drive (I didn't take the engine over 4800rpm) with the kickdown lever connected normally.
The OP's issue is the vacuum modulator, either low vacuum to it or the modulator is bad.

 

THe point was it was it was one thing or another....

 

When the E-Clip came off of my detent linkage, it got into a bind and shifted the exact same way. it would shift, but only after 4-5K RPM or so.

 

Finally got some daylight to check it out. The Vac line was disconnected from the Mod valve.

 

here is a question along the same lines. i have a 460/c6 in a motorhome w/ 30k miles. tranny will not shift to 3rd gear. running about 3200 rpm @ 60 mph. probably not redline, but wound up none the less. checked vacuum at manifold and vacuum modulator. fixed leaks and now has 18-20" vacuum at idle. replaced modulator. the old one did not leak, just eliminating the usual suspects. reverse works fine. the kick down is fine. it will shift from 1 to 2 but only when i take foot off gas. I was told by two tranny shops that this is a vacuum problem. it just seems that something else is binding. i don't think its the governor as it will down shift from 2 to 1 automatically. the fluid level is correct. i'm down to possibly the modulator valve itself is stuck ( i think some folks call this the shift shaft) or something gummed up in the valve body. (20 yr old rv and fluid likely never changed, and obviously sat for long periods) this though, is where the fun begins. i was going to drop pan and change fluid/filter and clean everything, but 2 pan bolts broke off. no leak problems, but ez out about 16 bolts doesn't sound like fun and may be better off to just replace tranny. was told by tranny shop to try penetrating oil and impact wrench and usually bolts will come out. havn't tried yet. could very easily have rust/ gummed up valve body, but have driven a couple hundred miles and would think that pressure/heat would free up. any other ideas? thanks in advance.

chris.