That's a given.
You're expecting alot out of the exhaust manufacture'rs.
They build exhaust systems to fit mutiple applications with one part number.
I highly doubt you'll find one specifically for a shortbox regular cab truck.
For one,the most common trucks are QC and CC trucks,not shortbox R/T's
Why are you having a hard time with this,buy yourself a hacksaw and use some tape wrapped around the pipe you need to cut,and go to town.
Or buy a system and find somebody to install it for you if you're not mechanically inclined.
It's not hard to change exhausts on new trucks,differant story maybe if the truck is 5 years old with a bunch of miles on it,but you'rs is new,so it'll come apart with just basic hand tools and some elbow grease.
I have the same basic truck,took me about 2 hours to change mine to a Magnaflow system,doing it on my back on my driveway by myself with nothing more then your standard handtools.
I do have a chopsaw,but i've cut many a pipe with-out one using a good old hacksaw and some effort.
This kit will fit your truck,read the application it fits Standard / Quad and Crew cab shortbox trucks,you just have to make it the length you want
Standard cab = Regular cab