If you are in Utah maybe see what randy's transmission could do for you. They are building 68's and may do some trading. Just an idea. I have his stage 1 in my 6.7, which is just tuned.
The biggest issue with the 68' imo in the last few years is the early low gear lock up tunes. If they lock up in 4th it saves a lot of problems, (hard shifting, speratic shifting, and input shafts). Also the like a lower gear. 3.73's and stock tires seemed about right. 3.42's and early lock up isn't the best for them. Then add line pressure at light throttle input and you have valve body issues.