Rsikes

Yes front dif has to be loosened up, and the pinion should be tight. 

Some of the bumpers has the cut outs for em and some don't. You'll need that bumper for them to mount properly,  headlight adjustments bolt into them as well. My 21 xt didn't have them, but had the cut out for em, simple, unbolt covers, bolt lights in and plug up. Wiring was there on my xt. 

I would go through and check/clean all the grounds.

I would leave towards the starter if it's dragging, normally a solenoid either works or doesn't, it wouldn't cause a drag condition.  

Xt vs xmr, with the same size tire, same tread pattern they'll ride basically identical,  the xmr is an inch wider, I've owned both, and currently have my 2nd limited.

May be a dumb question, but is it tied into a keyed ignition source? Or the battery direct?

bumper I built sat night when i got bored,  I'm really not sure how I feel about it, built it to have one a lil siffdifferent,  I normally run satv bumpers. 

Check your secondary rollers, it's usually the only problem the secondary have. 

I put em on the maverick Sport and trails also.

I change all the defenders out to turbo x3 belts,  longer life and stronger belt. 

The xmr defender will carry up to a 35 on stock clutching, just gotta know when to use low. As for tires, we have prolly 5 or 6 guys in our group running 35s on just jakes arms, if you want to run just 33s satvs or highlifter arms will do that will a lil less stress than the jakes. 

No I've had no noise as far as whistles or whines, I do know you'll get some hissing from the doors and windshield if you don't adjust them tighter.

23 limited, 8inch super atv portals, super atv foward a arms, kryptonite balljoints, quad boss 24inch wheels, 42 inch bkts, 2inch bracket lift, 4 rockford fosgate 6.5s, Memphis head unit with a Memphis 4channel amp, 1-10inch sub and box, with Memphis 750wat sub amp, curved light bar, rear light bar, whiskey throttle front link bars, thumper fab rear frame stiffner, evo stage 3 tune.

Maybe a lil more detail, seem to be slipping? Just low on power? What doesn't sound normal about it?

I run the maverick turbo x3 belts on all the ones I change out, lil more money, but a better belt for longevity. 

King Cobras  level 2s are beast, I ran them in my og maverick, and my old commander on 40s, no one else could make an alxe to hang out, only issues I ever had with cobras and most of the other top of the line axles, are the soft rubber boots eat themselves with harsh axle angle and high speed riding, and from the looks you have a pretty step axle angle. The factory axles and rhinos uses tpe boots, which hold up well, where the others use rubber in order to achieve the high articulating of their axles. 

The defenders has excellent clutching, with a lil common sense you should be able to run those 38s easily. I had a 21 xt on 42s with 45% portals, and never had a single issue, never a belt nothing. Have a buddy running 30% with 40s no issues, I have 42s on my limited now, no issues, I have a group of about 15 of us that all ride defenders, with no belt issues. Might want to check the alighnment on your clutch and make sure there's no rough grooves or anything in em.