Thanks for the warning.  I have a friend who was going to do 1 week on the trail (starting at the Canadian border and heading south) - he bailed after just 2 days due to the heat.  I'm from Houston, so heat is "normal" here, but I have a feeling it's gonna feel a lot worse at altitude. 

And in case anyone cares, I have decided to go with the Garmin Etrex 20x and my Caldera Cone alcohol stove.

[would the GDMBR be a good time to switch to canisters or will the alcohol stove serve me well?]

I will be attempting the GDMBR in a couple weeks and I have a couple questions:

I'm pretty simple when it comes to food - I only use the stove at night and even then, I simply boil water and add it in to something dehydrated.  I love my Caldera Cone alcohol stove, but I'm worried how difficult it will be to find denatured alcohol.  I've been thinking of getting a canister stove for some international trips - would the GDMBR be a good time to switch to canisters or will the alcohol stove serve me well?

I plan on having my phone with me, but prefer the simplicity of a dedicated GPS unit (keeping the phone available for emergencies).  I've been reading through the threads here and I see that the ETrex 20 & 30 are popular (particularly since you can pop in some new AA batteries).  Is this still the case?  Is there something else I should consider?