33x10.5(or 9.5's) and the 3.70's arn't all that bad, I ran my fj60 for a few years like that. I find the skinnier 33's don't suck as much power as a wide 33. With a lift I prefer the 33x10.5 vrs the 33x9.5. I did swap last year to 4.11 gears and it was certainly an improvment. The easiest swap will be to get the complete 3rd members from a 88-90 fj62, they are 4.10 and will bolt right up(you can prolly do this yourself) If you go with a ring and pinion swap then you "might" consider adding a locker to at least the rear, the install cost for the locker is almost nothing(more) when doing gears. If your asking the question, then you prolly can't or won't want to do a ring and pinion swap yourself.
another thing that will make a BIG difference in power is the condition of your motor as far as power, I'll tell ya, after I rebuilt my stock carb I got a BUNCH more power. If you carb has never been touched I would suspect the secondary(2nd barrel) prolly isn't working.....and with it working it will sure help move 33's alot better even with the 3.70's....especialy up hills
Cost wise, to swap in new(used) 3rd's from a fj62, prolly $400 for a pair of 3rds. then some seals, maybe bearings. Would be a good time to do a front axle overhaul.....if so add $$ If you go this route try to find a pair of front 3rd as they will prolly have less wear then a rear, might not have to replace the bearings this way
to replace(you take whole rig to shop) the ring and pinions. Prolly $400 for a new pair of gears, then install kits $200(pair), labor to install $600ish(both ends) Toss in a locker in the rear, $200-800 depending on lockers(see I can't open up a diff and NOT install a locker, seem like a waste of money not to

Then there are the little things that allways turn up that add cost.
Another option is to drop the 3rds yourself and have someone swap the gears, you will save a good bit on labor this way.
IMOP before I did a gear change I would get the motor in the best state of tune you can, if the carb needs a rebuild then do so, cost $300ish. Then go to the 33's, if your not happy then re-gear.
John H