Is there any downfall to changing just the upper mount? 
I ordered the TTR Upper mount and was wondering if I only change that one will it hurt anything else, like the transmission or lower mount? 
 
 
in simple, no, you will not damage anything
though I would suggest ALSO doing the lower mount.  theyre not that expensive and do more for you then the upper.
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Those so naive, so hard headed, so narcissistic, that think that buy their own efforts can single handedly change the world, are always the ones that do.
 
I might get the lower one in the future, but I have other things to buy right now.  
Thanks for the answer though.