Advice needed, Brand New C-18 tractive effort

I have one of the early delivered C-18s from Accucraft.

I have steamed it inside on my garage layout at 50F and on my newly completed outdoor layout at various temps under 40F. For each temperature and layout I have also used the same consist behind my slightly modified Ruby.
I'm a little disappointed in the C-18 compared to the Ruby. But it comes down to 2 things that can be addressed but I need advice from experienced steamers.

The first being steam, it will produce steam, and pop off. But it will run low of water if I leave the bypass open and will have to stop for a few minutes to steam up again after pumping in water again. If I close the bypass to an appropriate position to maintain water, it will barely stay above 20 psi, due to both the drag of the pump and the cool water going into the boiler. This performance was seen on treadmills too.
The first attempt to remedy this will be to check that the jet isn't plugged. I'm suspicious of this since there isn't much reaction to valve position past 1/2 turn. This is ceramic burner. I've used Butane normally and recently tried switching to isobutane. Besides cold weather gas pressure, I never saw an increase in steam from either engine. Anything else to check?

The second part of tractive effort after horsepower is traction. On the occasion that I have a full boiler, water pump in bypass, and steam to 60 psi. When I open the throttle I get lots of wheel slip with not much acceleration. With the same consist behind my Ruby, it will do a burn out, spinning the drivers as fast as it can. But the whole train accelerates at almost the same speed as a controlled start with no slip. Once it's moving about half cruising speed the wheels will grab again. I know one solution is to add weight to the engine, but it already weighs more than twice the Ruby so the weight per driver should be similar. The only other question could be the wheels, my Ruby has 2 1/2 years on it. Does that wear on the wheels give it a better grip than the brand new C-18 wheels? I am being generous with the oil on links and eccentrics and bearings, but the oil on the drivers should be no worse than the Ruby, and I try to keep the rolling surface of the tire clean.

Thanks for any advice.
Tyler