Truck stuck in 4 wheel drive

I need some advice my 2000 chevy silverado 1500 5.3L pickup truck will go into 4 wheel drive by itself sometimes w/out having to the auto 4 wheel drive button in .And it also pulls real hard to the right constently now the rear end is stuck in positive traction does it real bad in the rain

Any advice will be helpfull thank you

i dont know about the silverado but someone i work had an S-10 and the solenoids for the push button were notorious for going bad. about the posi-trac i have no idea