Jamblin

Ok, will do, but will have to wait for it to warm up a bit...

I wouldn't call it out thinking it. The only trans I know of that will downshift to compensate for a grade is the 6 speed Allison in my GMC pickup, if it is in tow/haul mode. All of the rest I've driven; GM and Mopar have stayed in the gear selected. If no else has seen this issue with this model trans under similar circumstances then the next thing to try is adjusting the throttle/kickdown cable.

Do you have the same tranny in yours?

If I shift into 3rd when it is in second with my foot off the gas, it shifts into 3rd. If I have my foot on the gas it is already in 3rd so nothing changes when I shift it into 3rd. I have 50+ years experience wrenching on cars and trucks and have worked as a mechanic and have never seen the situation where an auto trans would shift up beyond the selected gear unless the shift linkage was out of adjustment. My trans shifts crisply and feels solid in general. If others in Googleland have seen this non-standard behavior with this transmission they either just shrugged it off as a quirk or no one else has seen it. Since we would be more likely as a group to have downshifted on a downgrade to control speed, but no one else here seems to have run into it, I might have an outlier.

So, this does not make sense if this is as the factory designed it, especially on a 1 ton chassis where you would expect to be using engine breaking with or without a load. Every other truck I have driven with an auto trans does not shift beyond the gear selected unless the shift linkage was out of adjustment but this is usually obvious unless you always operate it in Drive, never manually downshifting. One test I might try is to temporarily disconnect the kickdown cable and see if it still does it. I've worked as a mechanic and been wrenching for 50 years and it does not seem to me that the shift linkage is out of adjustment since it shifts crisply between gears otherwise, but I will doublecheck it. @tstockma, I did post on yotatech a while back but got no responses so I gave it a bump.

I changed out the fluid and filter screen less than 100 miles ago and the fluid level is within the marks. The trans shifts smoothly with no slippage or other sign of distress. When I was going uphill it didn't happen but I was not fully releasing the gas. It operates normally in drive, with the shift points being affected by throttle position, so it will hold second if I have my foot into it and shift into the higher gear when I back off on the pedal. OD works but I only switch it on when I am on level ground at highway speed or on a gradual downhill to avoid bogging the engine.

Hmmm. Every other vehicle I have have driven would not go into a higher gear than the one selected, so that is an oddity that the throttle position would override the mechanical gear selector as a design decision.

The hill in question is 12 miles long at 6-7% grade so I have to use engine breaking to avoid frying the brakes. When I put it in 2nd to do so it shifts out of 2nd into 3rd unless I take my foot off the gas, which causes it to shift back into 2nd. With it in 2nd and foot off the gas it slows it down too much. Never seen an auto trans do this on any other vehicle except when the shift linkage was out of adjustment. The previous owner is deceased so I can't ask him about it. Even if the throttle kickdown cable was out of adjustment it that wouldn't seem to cause it to auto shift up to a higher gear than what is selected, but I guess I'll look at that next. Just wondering if anyone has run into this before.

I searched the forums and didn't see my particular issue so... My 1987 Sunrader (18 ft w/auto trans & OD 145k miles) has an issue with staying in 2nd gear when the shift lever is in the '2' position and it seems to be related to the throttle. If I am going down a steep hill and put it into 2nd, it will not stay there unless I take my foot completely off the gas. If I am giving it some pedal, it will shift into 3rd and if I subsequently release the gas pedal it will shift back into second. It also seem to do this on level ground, when using second to accelerate and get up to speed. Under those conditions I can start out in 1st and when I manually shift to 2nd it immediately does so, which appears to mean that the linkage adjustment is ok. Likewise, when off the gas it shifts down into second as it should when I move the shifter to position 2. From reading the Chilton and Haynes manuals it does not appear that there are any vacuum lines (i.e. modulator) running to the trans, which appears to be the A43. I read somewhere the the TPS may need adjustment but have not tried that yet as it is not easy to get to. Has anyone run into this or have any ideas?