Stag trip mileage, request for info

[Tim Buja <buja@domain.elided>]

Last weekend, Ann and I just got back from a 2378 mile trip in the Stag.
We drove up to the VTR National Convention in Hudson, Wisconsin, then
across the upper peninsula of Michigan and south to the Canadian
Classic in Sarnia, Ontario, then back home.  Here's some info on the
fuel consumption we observed while pulling a small utility trailer
(approximately 300 pounds) at speeds up to 65 mph.  I generally had
to use mid-grade (89 or 90 octane) fuel since 87 octane would knock at
3/4 to full throttle (timing set to spec at 4 ATDC at idle).

129.6 gallons (US) in 2378 miles = 18.34 mpg
1/2 quart of 20W50 motor oil
3 quarts of power steering fluid

Needless to say, I have to get the steering rack leak fixed soon.
Our Stag's engine was completely rebuilt last winter (bored .040"
over, with new TR7 exhaust valves, all new valve springs and guides,
reground intake valves, new jackshaft & 12 vane water pump).  The
lowest observed mpg over the 14 fill-ups was 15.22, and the highest
was 21.85.  The highest temperature gauge reading we saw had the tip
of the pointer at the left hand calibration mark at the top of the
gauge (just a touch counter-clockwise from straight up) while in a
traffic jam in Chicago.  

Now - a request for info from the collective wisdom of the list:

I just finished replacing the differential tonight since the original
differential was whining (and getting worse over time).  I noticed
that the driveshafts had a considerable amount of play to them, so I
pulled them apart to check the grease.  I found dried-up grey pasty
grease in the splines, so I cleaned everything up and regreased with
Castrol wheel bearing grease from the grease gun.  Is this the correct
type to use here?  I looked all through the ROM and there was no mention
of what type of grease to use in the halfshaft splines.  Do the splines
require a molybdenum disulphide type grease as used in FWD constant
velocity joints instead of the lithium based grease I added?  I did
notice a considerable reduction in the clunk I was getting when
initially selecting Drive or Reverse, as well as when changing from
Drive to Reverse or Reverse to Drive.  I did not notice any clunking
when the transmission changed from 3 to 2 or from 2 to 1 as I had
observed before I added the grease.

I'm getting a very bad lean stumble, even when fully warmed up.
Tonight, I noticed that while the right carb dashpot oil level is
normal, the left carb was empty.  Would the lack of oil in the
dashpot contribute to this problem, or is there something else that
I should look for, like a torn carb diagphragm?  I did notice that
during the trip, the trailer was blackened with soot from the tailpipes
and the insides of the pipes are black, not grey, so I don't think I've
got the carbs set too lean.  Both carbs were rebuilt just before the
engine seized in 1996, and I haven't touched them since.

Thanks in advance,
Tim Buja - Rockford, Illinois, USA - 80 TR8, 73 Stag, 72 TR6