P0456 can be caused by a loose gas cap. Make sure your gas cap is tight. I wouldnt worry about this check engine light until you get your DW solved. The P0456 shouldnt have any major side affects, as it is related to the fuel vapors and preventing it from evaporating from your tank.
check your wheel hubs. If you jack up a tire and try to wiggle it around and feel any play in it, replace the hubs. I'm thinking maybe the wheel spacers are applifying a problem that may have already been there, just easier to notice now.
Just a thought... I know a little play in a wheel hub can really throw the front end out.
Is it that necessary to get that done ASAP? I'm thinking the death wobble was caused by something else seeing how I was driving with the track bar in its original spot for days before this happened.
No, the location of the track bar won't cause the dw, it just centers the axle in relation to the body and gives lateral support to the suspension components, but loose or worn connections on the ends of the track bar will definitely cause dw.
Any play in the front trackbar bolt will cause or promote DW. Make sure the front trackbar axle end bolt is torque to 55 ft/lbs. Double check swaybar end link bolts or any front end bolts that were removed for the lift. As for the code, like others stated, check your gas cap and also check the evac canister and associated rubber vacuum hoses for cracks. There are some rubber hoses located under driver's side undercarriage that sometimes get deteriorated or missed when checking.
I know when you install a lift they suggest you tighten your track bar after the first 50 miles. Seeing as you had your disconnected during install you may want to re-tighten. I know that is what caused my DW. After I torqued down both sides of my TB (again) I haven't had any issues.
Figured out what it was once I had time to look it over. It is indeed my trackbar. The hole I had made intentionally for the new trackbar mount was too close to the old one. Even though I had just put it back it in the old one it broke a little bit if the metal bracket bridge in between the two holes, allowing it a little but if play back and forth with something as simple as me turning the wheel. Will patch it up with a welder, re tighten in the original hole, and hope that fixes it; which it should very well.
Your Jeep has the built-in ability to generate its own DTCs (diagnostic trouble codes), no need to buy a code reader. Just turn the ignition switch On-Off-On (not to Start) three times within five seconds & then wait after leaving it on the last time. Several seconds will pass before it will start displaying any stored DTCs so give it a little time.
Mine does not do that. No codes ever pop up even with a check light on.
Make Sure Everyone is Dead within hearing and sight range. Only then, you can say any area is cleared.
Tightened the trackbar. Fixed the constant DW. Still have a random DW thought that usually will happen right around 40-50 in 4th gear, normally Wi hint seconds after I shift into 4th. I haven't taken off my wheel spacers yet and I'm thinking that might be what's causing the remaining DW, will test that theory soon. Also CEL has cleared on its own after I tightened the gas cap and drove for awhile on it.
This is a long shot, check the fuel system for the code. This could also cause a wobble in the engine or a shake of sorts. It did in my 2001 tj.
make sure your steering gear box it good too. This caused a huge wobble in mine.
Turn your wheels left, turn off the jeep. check for free play in the wheel
do the same for the right side.
with someone under the jeep,
check your tie rod end on the drag link
check your bushings in the track bar.
tie rods/ ball joints
all this while someone shakes the wheel back and forth, a good 4 inches on the wheel.
make sure you have no torn boots on any parts
as Jerry said, make sure your spacers and wheels are torqued correctly.
make sure your tires are inflated properly, lets not forget a proper balancing on them either.
sway bar links look new,
I found when my gear box went bad, I was constantly steering left to go straight, when I turned my wheels left to park, I had excessively abnormal play in the steering wheel but the rest of the suspension components were tight.
when I changed my fuel sending unit, the engine shake went away.
Latest update, tightening the trackbar fixed the immediate and constant death wobble, and applying my transfer case lower kit eliminated the rest of the smaller vibrations. BUT, I still have the death wobble coming indefinitely from my front left tire at right about 40-45 Everytime. Usually when I hit a little bump is when it goes really crazy. Still trying to figure this last one out. My next bet is the wheel spacer possibly.