front end vibration/wobble

I got a 2000 Silverado 2500 4x4, 6 liter engine, 4l80E trans, with about 90K miles on it. Lately it has developed a front end vibration that I'm suspecting is turning into a wobble. Driving it I can hear it but I don't feel it. The vibration/wobble increases with speed. I've had it aligned and my tires balanced. I've also checked the tie rod ends, pitman arm, and idler arm and they are all fine. There are small leaks in the front diff seals but it hasn't run dry. (I filled about 3/4 quart last night). There is some play in the axles which I'm guessing is causing the vibration/wobble, how much play is normal? I'd appretiate any ideas on how to solve this problem, it's really getting annoying.

Thanks in advance.

When you step on your brakes if it pulses in and out it might be that your front rotors are warpped and that could be your problem causing vibration.

If anything stepping on the brakes makes it vibrate less. It also seem to vibrate less when I'm turning. I'm considering having my alignment checked again somewhere else.

Have you checked the wheel bearings? Mine started doing that, and I found out the wheel bearing had went out.

There is some play in the wheel axle on both sides of the diff, is there a good way to check the bearing w/o pulling the axle? How much play is normal?