2005 Chevy Silverado Hard shifts during long trips

I have a 2005 Chevrolet Silverado Z71 with 73000 miles on it. About two months ago, after driving about 50 or 60 miles, the transmission would shift very hard going from first to second and then from second to third. The truck ran fine and the problem didn't occur from third to fourth or during downshifting. It only occured while accelerating.

The check engine light came on and I drove home. For the next two weeks I only made short trips in the truck, 10 to 20 miles at most, and the problem never happened again. The second time it happened, I took it to the dealership and they flushed the trans and told me that if that didn't solve it, the valve body might need replacing. For about three weeks it ran great.

Yesterday, on the first 50-60 mile trip I made after getting the transmission flushed, the same problems arose. Again, on short trips it runs great, but long ones it has problems.

The dealership tells me that the valve body needs replacing and they "hope" that will fix the problem.

Will this work or am I looking at having to replace my transmission in the near future?

HELP?

Thanks

Kevin Serrett