I just bought new tires for my '91 K1500. The old front tires had worn unevenly...mostly on their outside edges. I figured it needed a wheel alignment so took it by the local Chevy dealership. The service writer said that the wheel alignment on this truck was not adjustable. He said he could remove the "knock-out plugs" and maybe improve the tire wear a bit but he recommended against it saying it usually made things worse and that it's better to leave it alone. Is this correct information? I've had problems with this dealership before so I'm skeptical of everything they tell me. Can the wheel alignment really not be adjusted on these trucks?