1990 F-150 front end

I have a 1990 F-150 2 wheel drive, the problem is when driving forward both front tires "toe in" real bad and wear out the outside edges of the tires to the cords in about 10,000 miles, but when you back the truck up as little as 10 feet both tires "toe-out so bad they almost look like they are about to fall off.
I took it to the shop and all they can find wrong with it is the drive side tie rod end is bad, all the ball joints, wheel bearings and even the I-beam bushings are good solid and no movement.

Any ideas on what might be causing this?

Replace the bad part then block a tire and use a flashlight and watch as some one else moves the steering wheel back and forth. It should be visible.

replaced the drivers side outter tie rod end, blocked a tire and had someone move the steering wheel and could not see anything move.
any other ideas ?

Take a 2 foot level and place it on the side of each tire in a vertical position. Watch the bubble on each side. Then check a friends vehicle and compare. You have to have the bottom on the same place on both vehicles. Some times these Fords have taken to a place that can bend the I beams.

Check the idler arm on the right hand side of the center link. If it moves up and down more than 1/2 inch replace it.

No idler arm on that type of front end,
checked it with the level and on level ground the tire's almost center bubble, back the truck up about 10 feet and the top of the both tires each go in about 2 1/2 inches and the bottom of each tire goes out about 2 inches.
have already replaces the I-beam bushings, 1 upper ball joint, a tie rod end and double checked the wheel beaings to make sure they are tight.

have had 3 other people looking under it when moving it forward and back and no one can see anything move.

also note, when driving it goes down the road straight, does not jump when hitting bumps or pot holes,

anyone have any other ideas :banghead: