Here's my experience with both;
I was a partner in a towing company in the early 90's, we had both Ford & GMC/chevy wreckers. The late 80's early 90's Fords never had any trans or rear problems. The late 80's / early 90's GMC did. We stopped buying the GMC's & stuck with Fords.
I will only have a Ford for towing my 7500 LB TT & 5000 LB Boat.
I have a 98 Lincoln Navigator (Expedition) w/ 107K miles on it for towing. I tow 8K-10K (back hoe & trailer & loaded dump trailer) with it, too. I'm happy with it's performance.