Gripshifter haters are alaways quick to advise junking them. Not sure why. I've been riding derailleur bikes since 1963, and the gripshifters on my Cannondale hybrid errand bike work as well as any shifters I've ever used.
I suggest checking for Youtube videos on troubleshooting those shifters. At worst, you'll have to buy a cheap replacement shifter. If you do get a replacement gripshifter for the front derailleur, make sure that it's the type with multiple clicks rather than the type with only two or three clicks.