My DT360  smokes excessively when it sits a while, and is first started.  After riding it for 3-4 minutes the smoke clears up.  After that I don't notice it smoking riding at 30-45 mph in the city but at 55-65 mph on the highway,  I can look in the mirrors and see a lot of smoke.  I also notice when the smoke starts, the engine starts stuttering and struggles for power. The bike has a Vape ignition system and cranks easily.  
I thought possibly a seal leak pulling in transmission oil, so I did a leak down test and it held 5 psi for 8 minutes and still had 3 psi at 20 minutes.
I checked my carburetor cable adjustment and the oil pump cable setting. The oil pump has less than 5 hours on it and was rebuilt and sealed by Deet. (It's working and I ain't unsealing it.)  

Any more ideas?
 

It's normal for the bike to smoke a lot for the first few minutes after starting. It should clear up once warmed up and revved out. If you just let it idle to warm up it will get "loaded up" with oil.
When the bike is shut off, the fuel and oil mixure naturally collects in the bottom of the engine, and the fuel evaporates and just leaves the oil.
Some manufacturers like suzuki created a system called SRIS to suck up this oil, but our humble DT Enduro bikes are just simple offroad oriented machines without the need for such complexities to satisfy emissions.

This is a oh shit, I'm going to piss off my neighbors smoke when I first crank it up and damn, I'm getting from behind this piece of shit motorcycle on the highway. Not normal.

My bike can smoke enough to upset anyone on my block when I first start it and take off...but it shortly clears up and stops smoking.
The engine smoking heavily and stuttering at higher speeds and not clearing up sounds like a rich condition or possibly a plugged oily muffler It can be caused by a clogged dirty air filter, or a faulty "jet setter" o-ring for the main jet. Double check the O ring. Try a 160-180 main jet for DT360.
Sorry if you've already tried these things mentioned elsewhere but that's the basics.

Leakdown will test in one direction.  The crank seal could still be leaking under vacuum.

The best way to tell is to monitor your gearbox oil,  If it's consuming oil without any leaks you can reasonably condemn the crank seal.

There should be no visible smoke once you're warmed up, cleaned out and at speed.  Maybe some under hard acceleration but none at a cruise.  My 74 uses what seems like a lot of oil, it's borderline excessive in my opinion, but I believe it's working as intended.

Have a look on the oil pump wheel, where  the cable is fixed.  In my case the clamp, which avoids the cable jump off, blocked the wheel from returning.  So oil pump supplies almost full throttle oil even at low rpm.

I pressure AND vacuum test so leakdown test can be done in both directions. Though usually if holds pressure will hold vacuum. Except the time it doesn’t. I got a deal on a DT175 because of this.  Previous owner spent fortune at shops and Yamaha dealer. Held pressure perfectly. Wouldn’t hold vacuum at all. Bad crank seal. 

That said, Powerdynamo tends to make engine run richer. Excessive oil smoke in my experience is due to rich air/fuel mix 99% of time. I’ve run 16:1 premix with virtually no smoke with bike jetted clean. Or 32:1 and it smokes bad when jetted a little rich. 

Keeping eye on trans oil and checking o-ring are all great things that should be done. Oil pump output check too. But ultimately you might need to fine tune jetting at throttle positions where rich.  Consult Mikuni manual to understand circuits and what throttle position they affect 

I used the wrong terminology. I did do a vacuum test and it held. I also checked the oil pump output this morning and it is good. I checked the transmission oil and It is good, however I haven't run this bike very long and I always back off once the smoke starts at highway speed. Unless someone offers another suggestion, I think I will do as AKARA1 suggested and check for a restriction in the exhaust and I have another carburetor I will install to eliminate this as an issue.

Have you had the primary crank gear off recently?  Perhaps the o ring behind the gear was left out or torn?

does not negate the wise advice to pressure test

Burnt the exhaust out recently. They get pretty oily right through. But once burnt out it should stay good if riding it at highway speed regularly. Can be a bit smokey on cold starting as your using the choke so extra fuel going through. Then again i guess extra fuel doesn't mean extra oil unless its on premix. So i don't know. Crankcase joint letting trans oil in. That's a bit radical & unlikely.