Currently have 31" tires and came across some rims with new tires for sale. But they are 33" so decently larger than I am running now.
Also I am using what I think are chevy/ford rims and seem to have a wider offset then stock suzuki rims.

So my question is, how do the stock rims compare to other offsets for rubbing on the frame? Looking at a set of 255/75/16 on suzuki rims but unsure about frame clearance.

Rig is 91 2dr sidekick with 4.5" alter ego suspension lift and 3" body lift.

And how about stress on the CV's etc... would one foresee rapid unscheduled disassembly of CV's or diffs? with 33"

If you get an offset further out does it help with frame clearance? Or hinder?

With your lift's there shouldn't be any problem getting them on.  They will take a more power to turn than the 31's you are currently running.  If you are running an automatic you could switch to 5.13 gears in your diff.s which will help with the power loss.  Also lower gears in the transfer case are a big help off road.  I have been running 33x12.5x15's for many years and haven't had many issues with the CV's.

I am running 3.5 inches back space on 15x8" rims.

With your lift's there shouldn't be any problem getting them on.  They will take a more power to turn than the 31's you are currently running.  If you are running an automatic you could switch to 5.13 gears in your diff.s which will help with the power loss.  Also lower gears in the transfer case are a big help off road.  I have been running 33x12.5x15's for many years and haven't had many issues with the CV's.

I am running 3.5 inches back space on 15x8" rims.

and running a2.7 v6....lol oops forgot to mention that ...right