In the past I have used Predator 10K antennas. These are really lightweight and have a nice bandwidth almost as good when I compared it to a 102" whip.
Power-wise, these antennas can handle anything you will throw at it. I recommend the longer shaft size of either 17" or 22". One draw back to the Predator antennas is they are taller than 5 feet depending on the model. I used the 22" single coil shaft and after tuning it measured nearly 80 inches.
Since you run a new Freightliner Cascadia, you did do the right thing and by-pass the factory coax. However, I would go one step further and use a different antenna mount.
If you look at other Cascadia's rolling down the road, you will see some drivers put a antenna on the mirror post using a custom "birds perch" antenna mounting bracket made specifically these trucks. These mounts will bring the antenna down lower so antenna height won't be an issue. I have seen one driver use a 102 inch whip with his but the antenna height was still over 13'6 which will mean a lot of bridge whacking especially if you run back east or Chicago.
These brackets can be purchased at most of the Flying J /Pilot truckstops in the CB radio accessories section. You can see in the pic above that it mounts to the 2 mounting bolts that secure the mirror post to the cab door. This will give you a better D.C. ground than the factory Teardrop mount you are using now.
You will have to re-route your coax. I have seen drivers run the coax under the cab and up and out thru the top corner of the hood. There is plenty of gap between the hood and the cab that the coax wont get crushed with the hood closed. This is currently how I route mine on a 2013 Volvo.
You should have a factory pre-formed hole under the cab where all the electrical wires enter the cab/sleeper but you will have to lift up the floor matting which should be able to be done by removing the threshold under the door.
You can also check the firewall for knockouts you can punch out for routing the cable out from the cab also for places to exit the coax out from the cab. These are places I have used in the past on other trucks to route coax outside without drilling holes.
Ask other drivers with Cascadias that use birdpirch brackets for more advice.
Good luck!