Toyota Repair: 96 Toyota 4x4 Tocoma, wheel tires, rims tires

Question
I have a 96 Toyota Tacoma 4x4 extended cab, 5 speed, 6 cyc 165,000 miles
I am experiencing a shimmy of some sort between 45 to 55 mhp
I have bought new rims & tires and also changed the front rotors and struts but the truck still shakes between 45-55 mph.
Any ideas for other items to check / change?  

Answer
It may be a driveshaft problem, especially since it is limited to this narrow vehicle speed range, can the vibration be felt in the seat and the whole vehicle or is it only in the steering wheel, tires normally cause a low frequency vibration, a driveshaft with a bad U-Joint or an out of balance condition will cause a higher frequency vibration, I assume that the new tires and wheels where correctly balanced on a computer balancer so I'm going to rule out the possibility that the tire/wheel combination is the problem, have the driveshaft checked for bad u-joints and have it balanced. Let me know if there is more information that may help me diagnose this.