Since you are new to the forum you might take a minute to try the search feature and learn how to use it. Please do not take this badly, but there are several awesome threads here already that discuss both of your concerns in depth.
A search on alko axles will answer your axle questions.
A search on d rated tires will talk about that.
Use the "search" menu selection on the "green" menu bar
Do not use too many search terms. It tries to match all of them and you could get no hits if you use too many.
Welcome to the forum and please enjoy your visit. Come back many times there is lots to learn and please contribute what you know!
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW