I am running 8.1.
I doubt the APN is the issue - and, I can't remember or find it in settings.
"What OS are you running, 8.1?
I ask, because since 8.x, on our phones, I have the *exact* opposite experience with texting, at one ski area we frequent.
While calling is almost impossible, due to very intermittent cell signal, if we text, it usually gets "pushed through", on one of the retries.
Occasionally, it times out, and I have to hit "retry", but I don't think I've ever had to do this more than once, in this location/situation.
I wonder if there's an issue with your APN or similar, maybe you're using a really old one for your carrier, and upgrading the APN would fix your issue.
I will say, I've tried to use Google Voice, to do exactly what you're attempting, on my W10m phone, and have had extremely poor success, and that's putting it nicely. While it works perfectly fine, when I have a nice strong cell or WiFi signal, as soon as things go "weak", GV fails to get my forwards, from my carrier's number.
Edit: Probably I should say GV fails to display the forwards, as obviously it's getting them still, just fine, but on an intermittent data connection, GV fails to display the forwarded texts and/or calls."