On a 2 inch level 33's with a MT tread design will definitely rub. A 275/60, 295/55, 285/60 with an AT design should be good to go. Don't think an AT 275/65, 295/60 or 305/55 will work without some rub.
1 inch spacer will raise the front 2 inches so set the 5100's at second notch which will raise the front an additional 3/4 inch. My experience with 2.5 inch level and the 5100's at zero lift is the ride is firmer than the 5100's at max lift. This may also be due to Toyo RT tires versus Toyo AT2 on old truck.
Had to take the truck in for rebalancing. Day before yesterday it developed a noticeable shake at speeds over 45 and the steering wheel was vibrating as well. One of the wheels had lost a stick on weight.
Another place to go is Horacio with Big H Customs on Old 83 about 1/2 block west of Ware Road. It's the place with the huge lifted Excursion out front. He's been doing lifts for 20+ years. Might help compare pricing, lift brands etc...
I recommend you save your money and do the lift, wheels and tires all at once. Get what suits your budget but do it in one shot. Truck is going to look like a hippo trying to dance ballet lifted with the OE wheels and tires. Besides you wouldn't buy a saddle if you didn't own a horse would you?
MO92's advice is pretty spot on. Additionally the options given with positive offset wheels will fill out the wheel wells more. Some have even done 295/60/20 or 305/55/20 tires with a 2.5 inch level kit on OE wheels or aftermarket with positive offset. YMMV
Bobber your brake controller install works for me. Since I sold my Yamaha Grizzly and the CRF450 before I traded my 14 AT for the 15 AT I wasn't concerned that it wasn't equipped with JL1. Have not towed but once with the 15 so I haven't installed my P3 controller. If I do install it will be in the pocket above the 4x4 switch. Banged my knee quite a few times with it in the 12 2500HD and swore never again to mount under dash.
At 5K to program/install a JL1 after the fact, OP would be better of:
1. Trade in truck for one already equipped with this option
2. Install aftermarket trailer brake controller
No way would I spend 5K for that.??
May work for some but longer legged people might bang their knees with it. If I did more towing buying a truck with JL1 option is a no brainer. Right now it is a non issue.
From what others have stated it is not possible to add the JL1 factory trailer brake controller if the truck does not come with it. If you want a quality brake controller get a Tekonsha P3 and put it in the pocket where OE one goes. Here is a picture
http://www.gm-trucks.com/forums/uploads/monthly_12_2015/post-127843-0-77143200-1448998330.jpg