everything is per spec
it runs amazing, idles perfectly, no pinging, pulls like a beast up to 6,000 then just falls off
I think pipe is pretty clean, but then again I never got it red hot
doesn't really bother me because at this speed the vibration from this large one-cylinder numbs my privates, but should it not pull up to redline or should I just chill and enjoy the super performance from idle up to 6k?
 

Is the jetting stock?  Ignition up to snuff?  IME the 360's are pretty much done by 6k-6.5k RPM, at least for the RTs.  

yes, stock jetting, stock ignition, timing double checked with strobe too

Again, not an issue, just a question on my quest to perfection!

If you have a stock air intake system in place and the tool tray on top I have found if you remove the tool tray that covers the intake vent you will get more power thru the entire RPM range.  Be happy with 6k with that beast.  It will melt if you spin it harder.  Mine is the same
Doug

Thanks Doug
I have zero intent to melt her again and I love this ride as is so I will move on!  But I might take the tool tray out just for kicks, although then I cannot proudly marvel at my stock tool kit! 

My 1978 dt400 lays down at 6k also but the tach says 9k rev limit. I guess it's best to shoot for the best performance up to 6k rpm.

Frank, it sounds like you have the wrong tachometer for you 400.
I think your 400 red lines at 7k rpm

I barely got it to 6.5k rpms and was fearing blowing it up. It just has nothing over 6k

The old instruments can be very inaccurate as well. I had an RD350 a few years ago that seemed ridiculously slow.  Getting to 55 was a struggle.

Mr Friendly Police Officer pulled me over during a test run and advised me I was going substantially over the 50 mph speed limit. Like go to jail speed. 

That was worst case I've seen but fixed speedo and all was good.  Verifying tach with an electronic tach and speedo with GPS is a good idea before trying to fix a problem that might not exist.

You know... when I go for a ride, I really don't like when it ends... So.. I'm not inclined to "race" to the end.. But then, I'm just getting started on this old hunk of iron..
Sneezles61