I have the same lift...
Lowering tire pressure will help and not affect mileage much (experience shows it will drop a tad though). But it could/will affect tread wear...The whole adding +10 PSI when going from PS to LT tires yadda, yadda - I'll attach a .pdf file I downloaded long ago that will help you figure out the approx right PSI setting. I have another one from Toyo (you can probably find it online) but it is too large to attach.
The lift you have is designed to work well with X amount of extra weight. Do you have a winch and/or dual batteries up front? If not my guess is you are under the rec'd weight for those springs. Same in the rear even with the bumper unless you have drawers with tools etc. in the rear.
I have the ARB up front with a M15K but no dual battery setup yet. In the rear I just have the Slee rear bumper (single swing arm). Ride quality is firm for sure. When towing the popup ride quality improves dramatically in the rear.
I'd talk to Christo and see what he suggests. But if you are done with the mods and adding weight, they yes, mediums sound like a better fit IMO. Load up the rear with some sand bags or something to see how it rides with more weight. I imagine the 2.5" heavy lift that you installed netted you more like 3-4" of lift and your ride quality is suffering.
I've read wonderful reviews about the FOR lift and how it rides like "buttah" all of the time. Never ridden in a rig with the FOR lift...Only local person I know who has that lift is Nay down in the Monument area.
Jeff Z. (the "not quite as skinny" one)
'97 LX450 - aka "The Whale"
'97 FZJ80 Antique Sage AE #267, stock
12/74 FJ40, 2F, SM420, 4" Lift, ARBs, 33" MTRs
"...anything else i can do for you guys, how about i wash your car or mow your lawn while you figure out your firewall system? I am now boarderline insane/unibomber." Kipper
"That assumes I'm even capable of pulling and stabbing..." Jacket
"I really like having a detachable unit." Beater