My truck is quite similar to yours. I have the same head and cam, actually. For a while I ran an LC Engineering intake tube and oversized exhaust, but returned to the factory plastic intake and OEM-type muffler, the drone irritated me. I ran 5.29 gears with 33" tires but have since returned to 30" and 4.10 stock 3rds. I have an Aussie in the back. I found none of it made much difference in reality. I did notice a performance hit going back to a quieter muffler. With the gearing, the RPMs were a little higher and it started from a stop better, but the overall performance was about the same. I cut off most of the armor, sliders, the heavy skids, etc. Shaving weight does help.
Our current path has been to replace it, there's a point when you just sort of realize that it's just not worth it anymore. It's the original reason why I bought this '91 in the first place, to replace an FJ40. I don't mind working on trucks, actually like to turn wrenches. But it got old spending evenings figuring out this or that so you could get to work tomorrow. Plus the constant tracking down parts from random places.
Old vehicles are almost always best complemented by a second vehicle that doesn't requirement much attention. When it's your only vehicle the dynamics change. If all my truck needed to do was trails and camping it would have been OK, but it's just so slow and uncomfortable on the highway and that's more and more of what it does. Also my poor truck has been worked pretty hard and has lots of nagging things wearing out. It was hit in a fender bender that to the insurance totaled it. Left a sizable dent in the side of the bed that is cosmetic, but just wasn't worth it for the insurance company to fix it. So that looks bad and is rusting.
I think the way to deal with these old truck is to (1) accept them for what they are, throw backs, or (b) update them. I was going through our desires in a truck and it turns out that it really wasn't going to be much more to get a nice, used Taco when considering doing an engine swap, semi-frame off restoration, body work, etc. I don't have the space to do it right and additionally I would need a car to get to work in the interim. It really pains me to cut Imelda The Wonder Truck loose, but that's the right thing at this point in life.
If time and money were no object I would do just as Skinny mentions, 3RZ swap. It's fairly straightforward. Or maybe a 4.3L Vortec. I'd take off the body, clean and paint the cab, probably go to a tray. Likely stick with 4.10 & 30" tires. Do a ton of sound proofing. Rebuild the suspension and steering, replace the carpet. Figure out how to install cruise control that isn't a stick shoved between the gas pedal and the seat... When I consider all that, add up the dollars and look at the time line, it was an "duh" moment when we test drove a lower mileage 2nd gen Taco. I know that it's not 1/2 the real truck my Pickup is, but man, it is so much nicer on Interstate and they're still pretty decent. Just took 30 second and pen stroke instead of a year of headaches. So far the only thing that really bothers me is the electronic shift t-case and that's just an FJC case-swap away from nirvana.