I want to upgrade my TAZ2 to a TAZ3 at least… the biggest thing I remember was going from a 12v to 24v heat bed + psu.
the 24v heat bed is not in stock on the store, I emailed support, who have never bothered to email back (support@lulzbot.com) (thats some awesome customer support right there), trying to find out when/if it would be back in stock… nada.
anyone know of any other compatible 24v heat beds of the same size I could use?
You should probably check your spam filters. Them not writing back is unusual. They do have the fully assembled with a PEI sheet beds in stock in 24v. https://www.lulzbot.com/store/parts/lulzbot-taz-heat-bed-kit
Here is the 12v to 24v upgrade proceedure:
https://ohai.lulzbot.com/project/taz_12v_to_24v/accessories/
Edit: there is also the refurbished assembly option:
http://i-t-w.com/parts/taz-5-4-3-24v-hotbed-with-heater-and-glass
You can also get the metal Y endplates and other parts there
I ended up getting the old style 24v heat bed from itw rather than the taz5 style one. need to figure ou t what else to upgrade to get to a taz3… slowly getting there! 
The threaded rod setup is different, but I think it still uses the same rods. Don’t go with the Taz 3 bed mounts, Print the Taz 5 ones, they don’t have the lifting issue and will fit fine. The Taz 5 X carriage is also going to be a drop in replacement with some additional nice features. The X end springs went through a bunch of revisions.Ideally you want to order a set of the X end plates from Either ITW if they get them back in stock, Or Techsavvy34 here in the forums, then pick up a pair of the leadscrews and leadscrew nuts (do a search for Mitsumi in the forums for the exact part numbers) and go straight to Taz 4 or 5 spec. The jump from 3 to for is a huge quality upgrade, and requires reprinting the same amount of parts. Assuming you have to buy them all new, thats around $120 + plastic for a much better printing printer
Edit: also, check your power supply. The Taz 1 was the 12 volt version, the Taz 2 should be 24 volt already.