I have been teaching myself QFT and General Relativity. The mathematics of those fields is daunting, and I find that what I have come across is very difficult to master. Of course it will take work, but can someone recommend a good text for self-leaning differential geometry with application to QFTs (particularly non-abelian guage theories) and GR? One that is clearly written and accessible to an amateur like myself. Thank you in advance.