So it won't even crank after it gets warm, hmmm. It could be 2 seperate problems with one being heat soak which would cause a stall and then perhaps an open circut in your starter which shows its ugly head when everything is hot. Interesting problem.
96 XJ, 3 in. Rustys full pack lift, 4.0, AW4, D35, C8.25
86 XJ, 3 in. RC, bb rear pack, 3.4 L engine