Electronics

I have a buddy whos' owned both, & Ive ridden them both lots. The Rancher seemed to me like a trail machine where the Foreman a work machine. I doubt the Foreman is faster top end if that matters. Might even have a rougher ride.

Foreman has more power and is bigger.  For someone your size, foreman will be better.   Rancher is more nimble and goes through the woods easier.   I'd say the 450 engines hold up a little better, but both are great engines.  I've had to replace cranks on 350's I've worked on.  Never had to do a 450 crank.   Both can be upgraded to disc brakes easily using Honda parts, and both can be made selectable 4wd (although as you said, if looking for a 450, the 02-04 would be the way to go because it already has selectable 4wd).   If I had to have one or the other, I'd get the 450, especially at your size.

Welcome aboard!  What part of MS are you in?  I'm across the river from Clarksdale in the Arkansas Delta.   Lots of 300 guys on this page.  

Again, the 01-04 Rubicons like you have are full time 4wd.  The newer 05-14 had selectable 4wd.  That's one big difference in the two, and the meters are definitely different.   You say that it runs good, but no ESP mode.   This transmission is a hydrostat, so that electric motor on the front of the engine is constantly moving, adjusting the swash plate on the hydrostat, so if it's not getting power, you're likely stuck with only being able to move at very low speeds.  Does that sound right?   The GPS units have an extra little plug hanging off of the back, and that little plug goes to a GPS unit.  3 plugs on this unit   https://www.partzilla.com/catalog/honda/atv/2004/trx500fga-a-rubicon-gpscape/meter-trx500fga-04   Regular units do not have the 3rd plug.   https://www.partzilla.com/catalog/honda/atv/2004/trx500fa-a-fourtrax-foreman-rubicon/meter-trx500fa-01-04   So I think you could use the non-GPS unit just fine.  I think if you get a GPS unit you'll also need to get the little GPS that plugs into it.   Make sense?   But yes, getting the proper meter is the first thing you need to do to get this machine running properly   Wiring schematics can be found in the back of the factory service manual.  You can download them free in PDF format from the toolbar at the top of the forum labled "service manuals"    

Hey I just wanted to introduce myself. I'm from MS and have a 1991 honda 300 trxfw I am currently rebuilding some stuff on it slowly, but it has been a great bike. Looking forward to the knowledge this place has. I'll post a pic of my bike once I get one.  Don't have one on my phone.