Vibration coming from the frontend. Put new tires on replaced both front axles. centered engine and tran.

may b wheel bearing

The question is the source of the vibration. Emissions issues may cause engine misfires and vibration. However, new ball joints suggests you experienced vibration in the steering wheel. Worn ball joints CAN cause this, but since replacement did not fix it, the next source is a worn inner CV joint on a front axle. This CV has to smoothly allow for suspension movement, and the concurrent in-out axle movement in the CV. What happens is the CV binds and generates wheel vibration, which can be severe. Have the garage check for wear in the inner CV carriers. Replace the axle if necessary.

Turn off the a/c & see if it still does it
Try dragging the brake while still on the gas to turn off
torque converter lock-up & see if changes
Check front drive axle CV Joints.
Check motor & trans axle mounts

Sounds like the axle isn't in all the way

You will need to check things logically. Run the truck in the air and note where the vibration is at. Take the wheels OFF and put a few lug nuts to hold the rotors on, take the truck to 45mph or whatever the vibration is the worst. is it still there? if its gone, check wheels/ tires. if its still there, check rotors, axles. A drive shaft will make a rapid vibration at low speeds since it turns 3 to 4 times faster than the wheels. does it vibrate on or off the gas? Can you power through the vibration like go 60 and then coast back through? You have replaced a lot of parts that would not cause vibrations. Are you just changing parts willy nilly or is someone actually checking and verifying that these parts really bad?

i agree that it could be the trans. when operating the vehicle, instead of putting it in drive, put it in 3rd. accelerate to 40-50. the vibration might be the result of the trans not being able to shift properly into overdrive (4th). if the vibration goes away, then suspect the trans, since the trans will no longer be able to shift into 4th. if the vibration is still there, suspect an axle out of balance since the speed of the axle will remain the same.

check out harmonic balancer .

Jack up the front end and put stands under it and block rear wheels. Look at axle boots and see if they are cracked. Try turning wheel back and forth sharply and see if you can hear any clicking. Problem could be outer axle joints. If the boots are cracked or you hear a clicking noise you will have to replace the axle. The axle and boot come as a complete unit. Please let me know what you find out.

I had similar problem with my '99 outback. Replaced the front half shafts and seemed much better. A few months later seemed to be comming back so replaced the driver side shaft again and the problem disappeared. I had put in rebuilt shafts and the driver side shaft was not rebuilt correctly.

I have been searching for a possible culprit on this and found the the WHEEL BEARING (inside the wheel hub assembly if I'm not mistaken) could be at fault. At low speeds you will feel/hear a sounds that seems to me coming from your tires (as if you had a flat, but you really don't) and it can cause vibration at higher speeds.