I’m kind of tired of buying a engine and running it right away.
I don’t know of anyone making HO scale diesel kits - assuming that by kit you mean a model where you have to completely assemble and paint it from a pile of components. These are more common over here in the UK, where at least two or three manufacturers produce diesel loco kits designed to use mechanisms from RTR locos - a bit like the old Rail Power kits, but with rather more assembly. If you’re interested, take a look at http://www.waveneycottage.co.uk/page8.html (Genesis Kits, they produce a few diesels in pewter) and also http://www.dckits.co.uk/ who make assorted railcar and other kits in plastic.
Yes;
See:
http://www.lynnet.com/~tigervalley/
http://bearlocomo.zoovy.com/category/hobbytown_kits/
http://www.bowser-trains.com/hoother/cary/cary.htm
http://djhmodelloco.co.uk/acatalog/
The TigerValley and HobbyTown have incredible pulling power due to thier weight, much more than any stock Athearn (including the DD40).
You may also find Front Range Products GP7 or GP9 and GSB SD40-2 kits on ebay.
This one is turbine, but it has a Cummins diesel inside for holsting moves.
http://www.resintrains.com/
Have fun.