Currently I own a GMC ENVOY, I am leasing an ENVOY XL DENALI for my wife, have previously leased a Trailblazer EXT, and my son owns a Jimmy. I have NEVER had any mechanical issues with the car. The Trailblazer EXT had one problem with the rear windshield wiper that was fixed immediately.
I dont see where these reliability issues are comming from.
Other than that one minor complaint Ive had only good luck w/ all of those GMC / Chevy SUVs