I too dealt with this years ago, at 30,000 miles and again at 55,000 miles on my 97 XLT supercab 4.6. I changed fluid at 30,000 to have the shudder reappear at 55,000 miles. I have been shudder free since 55,000 and now have 113,124 on my truck. The secret? I installed an auxillary tranny cooler to take care of the problem, along with fluid and filter changes once a year. I pull a pop-up camper three to four times a year, up to 1500 miles a trip. My drive to work daily goes up and down Signal mountain here in Chattanooga. No shudders at all since the addition of the 22,000# cooler from B&M. Bought it locally at Advance auto parts for about $55.00. Best investment I ever made. Just wish I had installed a temp indicator at the same time.
Oh well, Still have about another 150,000 to go. Maybe I will get to it.