I've had three endoscopies; you have nothing to worry about
! The test really is very easy. I barely remember anything, and each time I was told I would have a sore throat afterward, but I never did. I'm not sure if you've had an upper GI/barium swallow, but if you have, the endoscopy is much more pleasant than that. No yucky thick, chalky liquid.
As far as pH monitoring goes, be happy that you are avoiding the wires.
I too have a very strong gag reflex and had the test with the wire running up my nose and down my throat. Most uncomfortable 24 hours of my life! The nurse that did the test told me no one was ever late for their appointment to have the wire removed.