Cooper ST Maxx tires on 06 F350 dually in rear? sucks

[RamAirfreak98ss]

I replaced nearly balded Cooper Discoverer A/Ts 245/70/17s with
Cooper Discoverer S/T maxx 265/70/17 tires.. They're maybe an inch wider than the factory size 245s were.

The truck since last month, when i had the 4 back tires replaced, is all over the road. I don't mean a little, its nearly impossible to keep the truck tracking in a straight line. It fishtails all the time, 65mph on a dead flat dry highway feels like the tail end is wagging around... empty, loaded.. i won't even attempt to pull a trailer with it!

They're a more aggressive tire than the A/Ts were, but we have an 07 SRW f250 with Goodyear Duratracs which are brand new and just as aggressive and its no where nearly as bad as the dually is.

Anyone else run these tires? Anyone have a dually F350 with mudd tires, or something similarly aggressive?

Is it a rule of thumb they lose all their road holding capabilities with an all terrain tire? I'd assume any mud tire would be worse?

If you drive straight doing 50mph, and turn to the left then the right quickly, like just a little, you feel the back fishtail all over like a car on snow/ice with bald back tires but good front tires.. thats as good of an example as i can explain online.

What could be wrong? Bad tires? Bad choice of all terrains for the back of a dually? The width? I added 1.5" spacers a couple weeks ago and it didnt change anything.

80psi tires, dealer gave it back to me slightly over inflated at 85-90psi... i lowered them all to 75psi and it fishtails all over just like it did at 85+ psi. empty or 5000lbs in the bed it feels the same, just slower to fishtail with weight.

You all know what a truck feels like when spinning the back wheels on snow/rain on the roads... thats what this feels like all the time.

[NVHunter83]

Subscribed, as I want to get these for my 08 6.4l this fall. Looking for input....