04 F150 4x4

Noticed this yesterday morning, steering feels heavier than normal, almost like it is in 4 wheel drive. I suspect it is an IWE problem but haven't had a chance to check the vacuum. Gas mileage seems to have gone way down also.

Couple of questions:
On the 04's does the axle disengage from the front hubs in 2w drive? I did try and rotate the axle by hand when it was parked and it wouldn't turn. But I read elsewhere on here that the axles stay engaged full time.

Power steering fluid reservoir is full and there are no leaks or grinding noise from the pump.

Any other quick checks I can make to get me pointed in the right direction?

Prior to this I had an occasional bad vibration coming from the right front at around 60mph that got worse and worse. When it happened the first time I pulled over thinking the tire had come apart. I backed up a couple feet then got back on the road and it was gone. This leads me to believe I've got a 4x4 issue rather than a power steering problem.

Thanks for your help

 

IWE's default to locked. When vacuum is applied, they disengage. Therefore, with the engine off, they are engaged. With the engine running and in 2wd, they disengage. When you select 4wd, the vacuum to them is shut off.

 

Exactly the kind of info I was looking for