My 2002 F-250 SD currently has Monroe shocks on it that were put on in 2009 (45k miles ago)... They are shot and one seems to be leaking... Never again Monroe for me as the original ford factory shock...
I put Bilstein 4600s on my Suburban 2500 a week before a 2300 mile towing trip. Non towing seems to improve more than towing, but worth every penny. I called Bilstien customer service specifically for the 4600 vs. 5100 recommendation.