I wouldn't call it steering resistance per se. It's more like lag. Especially when on dry pavement. If you're turning to the right or the left, hard with locked hubs; the inner wheel on the turn has less rotations to make to cover distance than the outside wheel does. This gives the steering wheel a dead feel and is certainly less responsive.

Kevin that is only an issue if you are running a locker or you are actually engaged in 4wd.

As for the steering issue, id check out the power steering pump.

I agree Zach.

I converted the 98 ranger to manual hubs, left them engaged most of the winter. No difference in steering feel.
No dead steering feel in the 97 explorer with live axles, or the 05 sport trac with live axles and an aussie locker in front.
No sluggishness/ deal feeling with the hubs locked on my F150 (by unplugging the vacuum solenoid) either.

Any easy way to do that? Have someone turn the wheel and listen for noise? Or put a bar on the pump and listen for growling?

UPDATE
 

So I finally got frustrated enough to really check into the problem. Turns out that the u joints on the steering shaft to the rack and pinion were seized solid. SO $320 later my truck now drives like a brand new truck:D. The mechanic that diagnosed and fixed it told me that this is common on the F150's

I am experiencing the same symptoms, but I checked the u-joint on the steering shaft and it appears to working properly. I originally thought it was caused by the hubs being locked, but I just replace an IWE and the problem persists. Glad you got yours sorted out.

really? that seems crazy! but glad you got it fixed!

I told you it wasn't the hubs! Haha
Glad its fixed. I went through and replaced everything up front on my truck to fix some looseness. Finally figured out it was a worn out bushing or something on the drivers side of the steering rack. Replaced it with a reman rack but I could feel slight play in it too. A couple months later and it's almost as bad as my old one. I'm so frustrated. They will warranty the rack but I'd be screwed with laborand probably get another rack that wasn't properly overhauled. Ugh. Tons of money spent and it still sucks. Some days I just want to cut my losses and get a barebones gasser super duty with a real axle.

I thought so too. Turns out just the steering shaft is a $250 part.

I would go to the boneyard and see if you could find a rack from a crashed truck with low miles. I have little confidence in the 'remanned' racks that they just put new seals in.

Awesome Canadian_Screw,Thank you very much!! I had the exact same problem.I actually described it to a friend as feeling like driving with the front tires flat too..I did notice some rust around the pump and the swivel joint but didn't think too much of it.A couple shots of LP1 on the swivel and it's like new.Thanks again,that really made my day.Much appreciated.