I had a similar problem with my 2002 2.5 CRD (European spec) and the steering got progressively heavy. Turned out to be the ball bearing at the top of the steering column. I went to the various Jeep dealers here in SA to get a new bearing but was informed that the bearing was not replaceable and the whole steering column had to be replaced at a cost of about $2,200.00

When I had stopped laughing, I removed the steering column assembly myself, dis-assembled it to get the bearing out...it is 7mm thick, 37mm outside diameter, 25mm inside diameter deep grooved bearing. I bought an equivalent one from SKF or *** I think for about $4.00 I think.
I hope this is not your problem..lots of work, first check all the steering hydrolics and have a look at where the steering shaft connects inside the engine bay to the steering rack itself...check that the connection is tight and maybe have a good listen in that area while some turns the steering lock to lock with the engine not running.