XL chassis really shouldn't handle worse than the stock. You might need to play with different suspension settings, diff fluids, camber, tires etc to tweak the handling to your liking. I'd suggest playing with shock spacers and springs first as thats the easiest. For example, if you
watch my truck you can see its way too hard and on loose surface it makes it rather hard to control.
Wheelies, shouldn't be a prob. No probs with my build and that has a slipperential. Either not getting enough traction or slipper too loose, something like that.
The stock tires are rather crap, especially on loose surface. I just wish there was something in that size that had decent grip but didn't weigh too much. Not sure if i will stick with them on my build yet.
So far my truck seems to be a bit more ..graceful? in the air. I've only done a little jumping so far. Doesn't seem to get itself bent out of shape as easy and corrections can be made nps but maybe not quite as sharp as a stock length truck.
An alternative to XL axles would be to simply use offset wheels.
My truck still seems quite agile to drive. I know it's not the standard XL build but there should be some similarities. Best of luck getting your handling sorted, just dive in, change stuff and find out what works.