I have had a few instances where I've had my ignition/key lock where I cannot start my 2000 Chevy Silverado. The last time I fought with it for 45 mins before I could jiggle it free to start the truck. It will then work fine for a couple of months without a glitch. Anyone seen this before? Mechanic tells me not to replace ignition switch / tumbler just yet.

You're mechanic may be right. Sometimes if the steering wheel is locked you have to jiggle it while turning the key. I'd get a few opinions before shelling out though.

maybe your key is worn. Go to a dealer and order a new key for your truck.