When I engaged the 4WD the truck feels a bit sluggish driving in a straight line almost like the brakes are dragging. When making a turn it feels like things are binding up and the truck doesn't want to move at all. Felt like someone was standing on the brakes while I was giving it gas.
The first time it happened I didn't realize it was not wanting to move and gave it more gas only to hear a pop. I straightened out the wheel and it seemed to drive fine... except for the sluggish feeling.

A few days later while driving on the highway I heard a loud whining sound from the front that went away after about a mile. It was so loud the person I was talking to on the phone could easily hear it. It was in 2WD when this noise occurred.

Is this my Diff? maybe halfshafts? Any suggestions are appreciated.

 

Any 4x4 will bind up while turning if you are locked in and you have traction. All the more reason to leave the 4 wheel off untill you need it. When you turn and you have traction you're fighting basicly the same problem as if you had a spool and tried to turn. The pop you heard was probably some damage you did to your drivetrain.

 

I agree with landshark on this my buddy that has a 4 runner lifted has this happen to him if he forgets it in 4 wheel drive his front locker binds up hard!!

 

if they bind up can you go in reverseto prevent damage?

 

YES! Any time you engage the 4 wheel drive (front axle), you need to go in reverse at least a quarter-half turn of the axle to make sure the front axle is fully disengaged. If you stay in a straight line, engage 4x4, turn, bind up, then flip to 4x2, and continue forward, you'll keep binding. Go in reverse everytime to be safe!

The pop coulda been your transfer case, front diff, cv's, any of that stuff. A detailed visual inspection underneath should tell you what's going on. Look for grease that went flying from the CV boots, check for t-case leakage, also check for play on the front drive shaft.