Just installed new system, SWR is too high, please advise!

A high to low reading would indicate your antenna is still too short. If you have it maxed out it's either a ground plane issue or antenna length issue.

to give you context read over this page Grounds, RF & DC

edit: I'm waging ground plane issue if this is a mag mount rather than stud mount.

 

What do you mean about the ground?

It would help if you built an RF, not a DC ground. You are missing the RF ground.

 

I just now saw your picture. Is the painted surface your bracket is attached to the aluminum, or is that a Fibreglas layer over the metal? If that's the aluminum, you probably have plenty of functional "ground plane" for your antenna to work OK. At that point, it's apparently an antenna radiator length issue. Did you sand off some of the paint behind your mounting bracket? You might be able to obtain a longer piece of stainless spring steel to either replace or cobble on the existing whip, or the section below the loading coil. Lengthening either piece will have the effect of making the whip tune to a lower frequency, which is what you need here. I'd probably opt for getting a longer chunk of the "mast", which will raise your loading coil. That's a good thing: because of the distribution of RF across the length of the antenna, the higher up the loading coil is, the better.

Also, to make up for the roof being Fibreglas, you could invest $10 and get a roll of this self-adhesive copper tape. Stick a few runs of this stuff down to the roof in a pattern which will cover a bunch of the surface. Make sure to let them overlap some, or at least bring them all back to where you can fasten your bracket over the ends of them all, so they are electrically connected to the bracket. That'll help make up for the lack of a conductive surface that's parallel to the "real ground" (the road) and immediately below the feedpoint of the antenna.

Amazon.com

I did something similar to the roof of my 36-foot motorhome. I've got different lengths, all terminating at the antenna mount points. I operate from 7 to 440 MHz when I'm parked. CB is right at 27 MHz, and it works great.

The "ground" you ran from the antenna mount to the battery is a DC ground, not an RF ground. Nothing about the antenna system needs a DC ground. The two are not related.

 

That visor is barely big enough to be an adequate ground plane for 440 MHz, or maybe 220. An ideal ground plane would extend out to one-quarter wavelength (about 108 inches for CB) PLUS about 5%, or 113.4 inches/9.45 feet -- in all directions.
Since that obviously isn't an option on anything smaller than a really big van trailer roof (although still short out to the sides) you have to start figuring out where you can compromise. Your antenna's signal pattern is going to be strongest in the directions that have the most ground plane stretching out that way. Shorter than ideal is, unfortunately, kinda what one has to live with in the real world. Your pattern is already going to be worst to the rear; there's literally zero surface area behind the line where the antenna is mounted. But there will be some.
The rivets bonding the bracket to the aluminum shell will help somewhat. Keep in mind what will happen when dissimilar metals are put together: any amount of moisture will let the two metals form a battery of sorts, and will eventually corrode. If the rivets are SS, it shouldn't be a problem as quickly as if they were just steel going into aluminum.
The appearance of the copper (or shiny aluminum variant) will be a trade-off to go along with the enhanced performance. Even the best antenna detracts from the smooth lines of a nice truck cab for me. But we put up with it. If a metallic tape pattern were put on the roof neatly & symmetrically, kinda like a Japanese Rising Sun flag, it *would* invite some questions from other drivers, seeing the copper "rays" come over the top of the roof at the rear and converging on the antenna bracket.
Just about any CB antenna that can fit onto a truck cab is going to be a compromise in one way or another. Some folks have used a second, "simpler" CB antenna, like a FireStik, f'r instance, pointing downward from the mount to make a kind of vertical dipole, with varying degrees of success.
You'll probably have to experiment some to find what strikes the balance of what performance you need versus what aesthetic sense you can live with. There's nothing wrong with experimenting along the way. I've been a ham for 63 years now -- I started at age 9. CB'r since 17, commercial two-way tech since 25. My whole life in radio has included some element of experimentation.
Hope this helps.