Transmission Fluid Filter Change intervals

I have a 1999 Silverado Z71 Ext.Cab. I bought it used with 110,000 miles on it. The previous owner totaly screwed the pooch on the transmission. Hauled big horse trailers...never changed fluid. I had to have the transmission rebuilt by chevy dealer. Now, question is this. I know it is recommended to change transmission fluid and filter every 30,000 miles with normal fluid. I put synthetic in the rebuilt one, and was wondering if changing it every 50,000 would be sufficent now. Synthetic is a hell of alot more expensive!

I Have a 2001 Silverado and the owners manual says that you have to change the transmission fluid and filter every 50,000 miles, or 35,000 miles if you are towing/hauling often

I use syn. I love it. I go to 50,000 mi. It's a lot cheaper than a trans rebuild.