I have to add this too: From a practical user's point of view there is no good reason to convert a 34xx to 37xx, but there are in reverse. From a curiosity point of view it is interesting that original 34xx can convert to 37xx though.

One thing that has come out of all the results posted here particularly in [Only registered and activated users can see links. ] is that any earlier belief that 34xx and 34xx are uniformally identical hardware is unfounded. It does seem that they are reasonably compatible so far as fw cross-flashing is concerned but counter-intuitively and anecdotally in my personal experience it seems that the earlier 37xx have a GPS chip which handles the 34xx fw better than the chip in later production runs, although some 'unsatisfactory experiences' may perhaps simply be to do with software enhancement of accuracy not working. My personal theory is that the sw 'tricks' do not work. 'Hotfix' appears not to work properly in converts for initial 'lock on', so it's maybe reasonable to assume that other sw enhancements also don't work and therefore the cherished and constant fabled '3 m accuracy' reported by original 37xx is nothing but an illusion anyway.

It is easy and safe to flash back and forth with the 'Dummies' method though, and this thread was well named by Caty as as being for 'Dummies' because no real knowledge of fw is required.Anybody not sure of, or confused by, the unit's slow sat. lock on and/or reported accuracy in their 37>34 convert should read the thread linked above in particular the comparative test results described, and then replicate them the see the actual 'practical' accuracy of their convert using both this 'dummies' and kunix's alternate method from the other thread.