You might have too much gearing for a 4.0 with 33s. So that might be a consideration as well. You would be running around 3k rpm at 65 mph in 5th gear. Ideally you'd want to be 2300-2500 with the 4.0L.....I'd like to do an engine swap to get more power to improve driveability/going up hills (I have a 4.2L) and feel that the 4.0 would be the easiest way to get it and still stay legal and probably not much more difficult/expensive than another 2.5L swap.....
blitz: I don't know much about the smog nazi rules in CA but I am wondering if a 4.0 head with computer and fuel injection on your 258 (4.2) would be a simpler, cheaper way out if that doesn't violate the "rules."
To OP... I am driving a '89 with 2.5. It leaves a lot to be desired in torque for sure. As far as swapping in a 4.0 with your 4.10s, after driving the past few months with the 2.5 and 4.10 axles ratio, I am reconsidering my plans to stick with the 4.10s on my '91 project. The 91 is getting a 4.7 stroker (~284ci). With my 2.5, I run about 3000rpm at 60 mph which makes the 2.5 doable on the highway, but I am thinking I will get A LOT of gas savings with the 100+ horsepower and anticipated additional 140 ft lbs of torque geared down to 3.55s. Project plans are for 32 or 33s, max and I anticipate 95% DD road use so I think I can live with the loss of gear and enjoy the fuel savings.
For goots, you might want to accept the gas mileage loss though and stick with 4.10s or lower gears since it sounds like you do wheel often and crawling wants gear. Plus, you already have
the 4.10s so it is money not spent.
I say all that, goots, to make this observation: since you are getting married, taking the time and (relatively) small change to throw in a new oil pump, bearings, etc. to rebuild the 2.5 might be a good choice in your situation. Then save your coins for a planned upgrade down the road a piece. That way you are still on the road with minimal investment, a 'known' time investment, and peace in the fam as you work out a future with your wife to be.
Major upgrades to get where it sounds like you want to be are likely to not fit your current budget considerations. IMHO
I am 'new' to jeeps but I have been wrenching with pennies on various things for years. At 48, I have learned it is better to drive with a compromise with plans for improvements down the road than it is to get stuck running out of cash before I can get back to "driver" condition. A bonus to that I hadn't anticipated is that slowing things down brings the luxury of time- and that luxury has given me countless opportunities to obtain parts I needed for upgrades for little to no cost. I keep my eyes out and strike swiftly when an opportunity comes along. That's my advice- slow it down and get what you want without a big investment.