I'm betting he's mistaking the torque converter unlocking and locking for a shift between 3rd and 4th.
Here's what you can do to feel it out.
Cruise at 65 or so on level ground with O/D on. That should be 4th gear and just under 2500 RPM.
Now gently accellerate to 70, the torque converter will stay locked and the RPM should barely budge and you'll end up just over 2500 RPM. RPM increase should be in phase with the speed increase.
Return to 65, and this time try to get to 75 with half throttle or more. The RPMs should jump up around 3000 RPM as the converter unlocks, but speed will of course not jump as abruptly. Once you reach 75, back off the throttle and watch the RPMs fall, then settle again a second or two later as the converter locks up again.
Repeat once more (65-75), but this time as soon as the RPMs jump, turn the O/D off. The RPMs will jump a little more, but you'll be in 3rd with the converter locked up. Power will be more immediate, and the RPMs will increase in phase with your speed once it kicks down to third. Turn the O/D back on when you reach 75, and if you're not climbing a hill, the RPMs should fall in 2 stages again, once as it shifts to 4th and again just after as the converter locks up again.
Basically, if you think it's shifting, turn the O/D off. If it "shifts" again, the first "shift" was just the TC unlock, the second was the shift to 3rd gear. If you're in 3rd, 99% of the time you're guaranteed that the TC is locked up (which is better than 4th with it unlocked for any sustained period), there are only 2 ways to be in 3rd with the TC unlocked. One is if you're under 45 MPH, the TC won't lock up in 3rd or 4th...
The other time I can get into 3-unlocked is by turning the O/D off while climbing a moderate to steep grade (good) and turning the O/D back on before I reach the top (bad). The TC will unlock in 3rd and the RPMs will really wind up until you back off the throttle briefly and it drops to 4-unlocked (still bad, turn the O/D back off again and leave it off) or crest the hill and ease off. You DON'T want to run in 3-unlocked under load like this, period, the heat it generates is substantial. Don't turn the O/D back on until you've pretty much levelled out and can return to 4-locked quickly (2500 RPM at 65 MPH).
Brent
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