Hey just for the record:
I installed Energy upper front shock bushings, in stock at Autozone, and zero issues at all. Boy I feel stupid, but in most other applications poly is the wrong material. Perfect here for almost a year.
I replaced the bushings on the motor mounts with...
I am 1000% sure it's not at the limits of the shocks, I measured it.
I destroyed the bushings that came with the shocks
OEM-type replacements from the auto parts that came with Monroe shocks
Literally 15 sets of the rubber Dorman replacements
I found a dusty old package of Energy Suspension...
It's the heat doing it, geometry is perfect and it happens just driving down the highway, not just bouncing all over the place on a trail. I tried some redneckery - aluminum foil, towel, etc. The fenderwell sheetmetal just gets hot and there they go.
I've been running my LS-swapped XJ for a year and have put lots of on and offroad miles on it. It eats front upper shock bushings. I mean eats them. I've tried poly, they last about a day on the trail. I've used many rubber bushings from different auto parts stores and they are clearly made...
People don't realize that almost all of these fabricated Al radiators use pretty subpar cores (even if they are thicker), and the fabricated tanks are even more prone to cracking due to the shape of the XJ's radiator. You want high density fins and a strong fan.
That exhaust is mean. Glad I don't like in Cali :) Are you getting any other codes at all or what's all turned off? As far as trans tuning goes, a 6L80 is a different beast so don't let just any id10t tune it. You never have to take the TCM out of the trans to program it, either. Do you...
What are you doing for mufflers and stuff? Cats, I assume? I have to figure mine out soon because I don't want a loud exhaust on it. I have a G8 with a TVS2300 on it and other goodies and it's hard to keep it quiet.
It must be using the tach output on pin black/48 then? That's a pretty basic circuit, but I don't know what's in the Novak box. It needs a pullup resistor on the input to the box, and somewhere the chrysler bus needs a terminating resistor or two depending. But you said you never removed any...
If you wig out one of the modules on the bus it can pull the bus hi or lo and not release it and it prevents the other modules from talking to each other and it throws the code. They weren't very smart back then.