I would go with the AF - however I might be a little biased -but my 22H has been trouble free since 2005. I kept an 86 Komfort for 13 troublefree years until trading it for a Trail Lite which was nothing but trouble - I traded it in 05 for the AF and love it. If you want to hear more about the AF go to www.afnash.com
and look at our forum. We have several people who take their TTs into the real backwoods and for the most part, the TTs hold up real well - most have larger ground clearance than most. We also have several members in the Spokane area.
As for your truck even with the age it is still a good truck. They don't make em like that any more - that said you might find that old 350 sucking sand when towing much over 5000 lbs. I had a 99 Tahoe with an improved version of the 350 in your truck and it was difficult to climb hills and even get up to HY speeds. Now with my new truck I hardly know the TT is back there - is also has 4.11 gears - which would have helped the old Tahoe.
As for dealers - NW RVs in Spokane is a Northwoods dealer you can probably do better at Broadmore in the Tri Cities or Thunder in La Grande. In the past, NW has put non customers to the bottom of the list when it comes to repair work - esp warranty - with Northwood this is not really a problem as they can authorize other shops to handle warranty repairs - you just need to contact Northwoods ahead of time to work out the details - maybe they can also arm twist NW.