I just bought a 1994 4Runner (124,900 miles original, lots of work just done i.e. new head gaskets, new timing, new motor, new radiator, etc.) and when I am in 4wd and attempt a turn sharper than a half turn of the steering wheel, the steering starts to resist and the car slows down a lot and the tires seem to shake and it almost feels like some of the gears are slipping, however I am not a mechanic so I don't know for sure if that is what is happening. The car is perfectly fine when in 2wd but if anyone can give me some advice I'd appreciate it.

 

Newer 4WD vehicles use an additional differential gear between the front wheel drive and the rear wheel drive to avoid this issue when driving on surfaces that don't allow for the different rotation speeds of the inner and outer tires when turning. To avoid this binding (which is not good for your transmision) the solution is to either make sure you take it out of 4WD before you drive on dry pavement or just trade in on a newer 4Runner (the later models like my 2005 have this added diff with a lock/unlock switch).

 

What you describe is normal. Like jgrant721 says. Why would you want to drive in 4wd on dry pavement?