Hello again!
I now have a pretty good running Coleman UT400 after a top end rebuild, wet clutch rebuild and a repaired crankcase... !
It plows snow great, but I was also having the jumping out of gear problem, mainly reverse, but a couple times out of forward. I would quickly place it in N and then let the engine idle down and shift again. This worked most of the time.
I did some research and found that some have modified the shift linkage. The problem with just adjusting the shift cable is that it really NEEDS more throw, not an adjustment. From what I've read and viewed on the Internet, the linkage arm needs to be about 3/4" longer to gain more throw in both directions.
On YouTube, the guy had to remove the shift linkage hole trim and notch the side of the dash to get the shift linkage off the pivot pin. BUT this is NOT necessary. When the "E" clip has been removed and you fish it out of the firewall somewhere, the shift lever is now loose. I had to pop the top of the shift knob off, remove the retaining screw and then heat the lower portion of the knob to get it to come off the lever. Once you have the shift lever loose, push it towards the right to slide it off the pivot shaft. But it won't come off just yet. Use a small pry bar/screw driver and slide the nylon flanged bushing out of the left side of the lever. This lets the lever slide off and get into a "loose" condition and it will twist and come right off without removing the dash trim, that could be a bugger to get back on correctly.
Once the lever is off, press out the other bushing so when you're welding on the linkage arm, you don't melt the bushing. I found a piece of scrap metal the same thickness as the lever arm, just over 1/8" thick, close to 3/16". I cut my arm and beveled the edges for better welding. I added a piece just over 5/8" long and kept about a 1/16" gap between the arm and the new piece. Once welded on bother ends, it adds up to just about 3/4" or so. I reinstalled the lever after painting it and did an adjustment on the cable. By the way, it's easier to remove the cable from the bracket on the frame. This gives you more clearance to maneuver in that area with your hands. ALSO, you will need to get a 12" adjustable wrench and slide it over the cable mounting bracket and tweak, to the front, the steel so the cable is pointed upward a bit to now realign with the new longer shift arm lever. There's more than enough metal for the tweak and it will line up perfectly.
I now bottom out the shifter on the transmission BEFORE I run out of throw on the shifter... I've tested it just a bit so far and it shifts much better with the longer throw. One of the Coleman authorized repair facilities said that he worked with Coleman to get a new part that's longer by 3/4". He's modified a few and it works perfectly for him. Just doing the cable will just short you on the other end.
Here's some pictures of my modified shift lever etc.