I had a gas 190XT for a few years used to bale with it,burned about 4 gal/hour

Keep the diesel for now to use while you have the gasser torn down for repairs. Once the gasser is fixed, then decide whether or not to keep the diesel.

The difference in fuel costs at ~150 hours per year total time on all of your tractors will be a minor part of your total operating expenses. JMHO, your mileage may vary

But despite all that, if I was in your shoes I'd probably be doing the opposite of everything you're thinking. From your current and previous posts on here, it sounds like you're not into collecting nor strictly looking for oddball/rare units. You want a 190-sized tractor to be your primary large tractor on your farm. And given that the diesel is recently rebuilt, is mated to the better tranny, and has the three-point, it would be a great all-around unit and serve you for many years.

For only 150 hours a year, the gas vs. diesel is more personal preference. But I'd definitely be keeping the three-point on whatever unit I kept. While I applaud your desire to be an Allis purist and stick with the snap-coupler, you're limiting yourself to a very, very narrow sub-set of Allis implements from a very specific time period. With a three point, you're opening up your implement possibilities to everything made by pretty much every manufacturer, ever.

Even if you want to stick with Allis implements, for any implements appropriately-sized for a 190 you'll have far better luck finding Allis three-point implements rather than snap-coupler. It would be different if this were a D17 or smaller, because there are still lots of smaller snap-coupler implements that size out there. But most implements sized for a D17 or smaller will be waaaay too small for a 190. Snap coupler implements large enough for a 190 are few and far between, and getting rarer every day. Whereas three-point implements that size (including Allis implements) are readily-available. It's worth considering the long-term: What happens if in 10 years you wanted to buy a mower, bush hog, mounted tillage unit, or any other implement?

Regardless of which you keep, I'd also try to fix the gear-jumping issue without splitting it or tearing apart the tranny. As others have mentioned, there are a few common fixes for gear-jumping issues that can be done quickly/easily by just pulling the top cover, and they usually fix the issue. I'll confess, however, that I'd never done these for a 190 - only for 180 and smaller. But the theory/procedure should be the same:

i) Turn the shift rod and grind a new detent spot for more engagement. The Allis service bulletin for the 185 suggested only 0.060", but like others have said above, I strongly recommend going deeper (at least 0.100") if you have the stroke. Agco used to sell deep-shift rods for the smaller tractors. Not sure if they ever did for the 190, and they stopped offering them for the smaller tractors a few years ago, so I'm sure you're limited to modifying your old one. Pretty quick/easy to do.

ii) Replace the detent ball spring with a stiffer/stronger spring (Dr. Allis has alternatively suggested putting a second spring inside the original).

iii) Replace the shift fork for 3rd/4th: The original forks didn't have a lot of meat on the engagement surfaces and got worn down. They also didn't have much reinforcement to prevent the 'prongs' from bending. They'd bend/wear over time and not engage the gears as deeply. The new shift forks are a little beefier. The 190 uses the same 3rd/4th shift fork as the 180/185, and they're still available (DJS has them for $100). If you do end up putting a new shift fork in, make sure you do that and check how much extra stroke you have before grinding a new detent spot (you might find you have less extra stroke after replacing the shift fork).

The only reason I can see to sell the diesel instead of the gasser is if you really need the cash. A diesel 190 with a rebuilt engine, good tranny, and three-point is still a very useful/desirable tractor and will fetch a good price. A 190 gasser with a snap-coupler and jumping tranny would bring little more than scrap price around here. But regardless of that: Using the potential selling price to decide which to keep would be pretty short-term planning in my opinion: You'll never get a tractor that size cheaper/easier than the ones you already have. So if you plan on keeping one for a while, better keep the best one.

My vote: Try popping the cover off the gasser's tranny and doing the quick/easy gear jumping repairs mentioned above. If you can fix the tranny jumping, it's at least somewhat sellable, and also more convenient (and safer) if you end up keeping it. Then use them both for a bit and decide which you like best. And I strongly suggest keeping the three-point on whatever one you keep.