I definitely know what you mean by a tight fit. My 2005 Northstar Igloo barely, barely fit my 2010 Dodge. I had about 1 1/2 inch of clearance on both wheel wells, but the bathroom bumpout only cleared the tailgate opening by about 1/4 inch. Tailgate openings on current trucks are about 60 inches for Dodge and Ford and about 58 1/2 for Chevy.
I did not have any issues with the diesel controlling slow movements. It does take a foot on the brake to back up slowly and evening. My issue was alignment. I tried several techniques. The best was a laser level from Lowe's. It has a strong magnetic base that attaches to the wheel well with the laser pointing straight backwards.