Hello all,  I have a 81 Jeep CJ8 with the ZZ4 350, TH350 tranny, Dana 300 transfer case in it.  I went wheeling this last weekend all worked fine 2wd, 4wd all weekend.  Drove back to camp from the trails in 2wd hubs unlocked and parked it for the night.  Next day pulling out of camp for the ride home and shifted into drive and only got the first gear.  Park, neutral, reverse work as they should. I have the B&M truck shifter and I tried ratcheting into 2nd and 1st out of drive and no shift, just stays in first.  Made sure transfer case was where it should be, worked through 2 and 4 wheel high/ low and thats working fine. Drove it down the road dropped into neutral back into drive everything I could think of. I know about all other workings of the jeep but the TH350 and auto tranny's is something I know very little about.    
 Any starting point would be greatly appreciated.  Thanks.  

Check your cable linkage underneath for any broken brackets.  Also check at the transmission joint were linkage meets.

I would also take cover off of your B&M shifter to see if anything is jammed in there.  Use some WD40 to lube it any moving parts and cable.

If none of that works, You might try shifting it manually at the transmission--just don't run over yourself.  Maybe have a transmission shop check it out if it gets to that point.

I also have a TH350.  

I would check TV cable and vacuum modulator. If it is either it will still over ride shift into next gear if you rev it high enough in gear. (unless you disabled it with shift kit). If TV cable is broken, tranny will think it is WOT and will not want to shift until maybe 5000 RPM or more with a stock tranny.  

I have checked the shifter cable at both ends, it moves fine through the different points.  I looked at the lower end of the cable at the tranny and it's moving the shaft out of the tranny just fine. Still have to check the vaccum to the tranny. The kick down cable is fine also not pulling up on the plunger. I havent tried reving the engine past 4000 rpm yet just figured it would have shifted by that point. The only external piece left I guess is the vaccum modulator. Not sure how to test to see if it's bad other than a part change.  If not maybe into the shop?  

Check your nylon gear on the governor, it under the dust cap towards the rear off the trans case. If the gear is missing a couple teeth (striped off) the trans wont up shift. It has happend to me. Good luck.  

most likely the governor there,although first check the vacuum hose, use a bar/large screwdriver and a hammer to pound off the round stamped sheetmetal cover, pull out the governor, check the gear, also be sure the valve isn't stuck... it'll dump about a pint of fluid is all.

if it was a vacuum or stuck tv cable it would still shift at a very high rpm.  

I Found It, it was the governor gear . It was missing teeth and in bad shape.  My question now is if those plastic pieces broke off will the tranny need to be flushed or will those pieces break up and get stuck in the filter?  If so maybe just replace the filter and the fluid?  Question of the day.    

Oh and it did dump a little fluid when I poped off the cover, not a ton maybe a 1/2 qt.  

they won't plug the filter, although It'll be a good idea to go ahead and change the oil and filter. the chunks can get in between the pan and filter and rip a screen type filter.

use a fiber filter not a screen filter....