91 K1500 sagging?

Check the cab mounts.

-- Best Regards Gordie

never thought of that. but it seems that the fender-gap on the left side of the truck has decreased front and rear....almost more to the front.

what should I be looking for in terms of the cab mount?

When it get real bad you can see a rusty area tight where your left foot touches the side when you drive. The seam along the floor would be affected. I had a Chevy where you could actually see down to the ground under the door hinges when you open the driver's door. That view goes all the way down through the cab mount underneath. My '80 Chevy is open to view but after 1981 they included a tray made of plastic that covered from the rear bottom of the front inner fender and attached also to the front cab mount that I am trying desperately to describe :)

Under the truck in the area where the door hinges are is the cab mount. You should be able to see if it is rusted away or crushed or both. It can be repaired. When in doubt, kick some tires at the local dealership and slide under a new one to see what one might look like.

I only mention it because the winter salt used in my area makes for lots of rust in this area. You would sit in the Donut Hole and gaze into the parking lot only to see your truck sitting low on the driver's front corner and it would bug you bad enough to take a tape measure and check from the frame to the ground only to find that the frame is pretty close to level. Someone had to tell me about it. I didn't know what to look for.

-- Best Regards Gordie