Just one thought against the N+1 (or 2, in this case). Perhaps if the Tahoes are performing adequately, they'll buy plenty of riding time while you sort through the collective knowledge here, and at your local shops.

I just think an MTB is the one bike I have to have because of the extreme weather and less than ideal road condition where I live. YMMV. They'd make great limestone trail bikes for you now, while you decide on your next step. I have a skinny tired, too fast, lightweight also, and it's my preferred ride, but when the chips are down the MTB gets the call for the day. Remember, around here it's "N+1" not "N-1+1".