Runs great in gears 1,2,3 then really sluggish when I hit 4th at 40 mph or so. doing some research might be a weak source coil, so I've been thinking about going to a Vape CDI and 12 V conversion

I'm in Canada, don't believe this is an import. but likely the same logic applies. Good to know thx!

Canadian will have a Canadian approval decal on the steering head. 

Should have points.  Very reliable system in most cases.  If you do splurge on a CDI, your original ignition system is sought after to replace the problematic 360/400 original CDI

We've found on some Canadian models that the VIN numbers extend beyond those shown for the US bikes in the VIN tables in the Tech Library here.

I've got a Suzuki GT550J that was imported from Canada (I'm in the UK) and it has the type of decal that Mark was referring to.

First port of call for lack of performance is often exhaust in the tail muffler. I'm stuck on exhaust lately so it seems. Don't go throwing money away on other things until you've eliminated the usual stuff--should go like a rocket. Cheers from NZ.

RT325  can you expand on what to look for with the muffler/exhaust issue?

Pretty bike!

In addition to exhaust I would clean and check all aspects of carb such as jet sizes, etc and also make sure gas is flowing well out of tank at line into carb to make sure she's not starving. 

I am restoring a Dt1E and due to a meltdown lesson learned on my dt360 I decided to check crank seals and both seals lips crumbled vs flexed. Doesn't sound like you have a pinging issue but still maybe something to check out once you can zip up to top speed. 

where did you find this one?

good luck with it!!