Those can be a bear when they've never been apart before. Apart from making sure to use a second wrench to hold the tie rod end in place use a length of pipe as a cheater bar on the wrench you're using on the nut. Also it might help to clean the dirt out of the small gap between the jam nut and tie rod end and get some pb blaster in there. Clean the threads on the other end and spray there as well. More heat on that nut should really help too if you're not getting it hot enough. You can always use MAPP gas to get that nut glowing.
When you reinstall, be sure to smear some grease on the clean threads where the jam nut will be resting against the tie rod end. This will prevent problems in the future and basic hand wrenches will be good enough then.