I am set at Wide/25KHz under Bandwidth setting.
OK, that's good.
I adjusted Mic gain (range 0-127) from 10 to 15, no luck.
OK, that's something you can adjust as you get a bit farther down the road.
It is a UHF antenna designed and factory tuned for GMRS freqs. It's mounded using a under eaves pole that wrap out around my gutter. It's about 5' above my roof which is about 30' from ground level. I did not ground it yet using any ground rod (i plan to but haven't had the ability yet). I do not have a SWR meter yet either, wasn't sure what one to buy. It's a 50' rg8x coax (bought off amazon). Connectors are solid.
Do you have a brand/model number?
If it's a mobile style antenna, it'll need a ground plane under it, like what you'd get if you mounted it on the roof of your car. For a mobile antenna in a base environment, this would have 3 or 4 radials coming off the base of the antenna mount horizontally.
If it's a mobile antenna just mounted to the offset mount, then you'll need to address that.
If it's a real base antenna, then it should be OK.
RG-8 isn't ideal coaxial cable for UHF applications when the run is that long. But it'll work if you are in range of the repeater. I used some RG-8 for a while when I was active on GMRS and it was fine. Ideally you'd want to use a shorter run or higher grade cable, but don't go spending money on that just yet.
An SWR meter will help you confirm your antenna is working correctly. It's a good investment. A basic UHF SWR meter will suffice.