Engine revs like in neutral while in gear
 

I have a 2002 4wd s10 and heard a sound as if metal on metal scraping coming from under vehicle. It started at around 25 mph and up while accelerating and driving. However when I took my foot off the gas it would cease. Then while driving at around 55 mph something happened and my speedometer flew past 100 mph while I coasted on the freeway. Basically the vehicle revs as it would in neutral although it is in drive. Any thoughts?
Also when the tow driver dropped it in my driveway and proceeded to leave it started rolling after him down the driveway (while in park). He pushed it back up and just put the e brake on.

I'll bet the transfer case or the rear diff went - during testing block the front wheels well and release the parking brake - #1 try to turn the drive shaft with transmission in neutral - if it won't turn diff might be OK - #2 put transmission in park and jack a rear wheel up off the ground, turn the wheel or the drive line, if the drive line will turn I would guess the transfer case most likely went out - :icon_shrug: