chevy truck help??

So since my wagon is waiting for a transmission ive been driving the Burb and I have a problem now. Its stuck in park!

Truck is a 1999 Chevy Suburban 2500, 4x4, Diesel. Its stuck in Park. I tried pushing it forward with my friend in the truck to put it in gear, that didnt work. Brake lights DO come on so I dont think its the brake switch.. whats the problem? Any ideas? Thanks guys.. -Paul

Is the truck on an incline? I would think it is the brake neutral safty switch.

Climb under and make sure the linkage isn't broken or binding. I know that's where I'd look before I start checking switches and sensors. Try manually putting it into gear at the trans and that'll tell you if there's something wrong internally or externally.

With the key on and engine off step on the brake pedal and listen for the faint click of the shifter release solenoid.
The wagon did the same thing when i bought it and it was a bad connection at the brake switch.