(ET) Energy usage

["Banks, Michael J." <mbanks protopower com>]

The past couple of times I have mowed the lawn, the track seems to be
using more energy than usual.  I have an E12.  I usually mow in D
(DD,D,N,L,LL using this as the gear progression, LL as the lowest).
Since I have had the tractor, mowing in this gear the Power Meter
usually hovers somewhere in the low to mid yellow, rarely in the green.
Lately it is up toward the high yellow, sometimes in the red.

The front tires might be a little low on air, it is hard to tell (I
haven't used a pressure guage).    Would low air pressure in the front
cause the tractor to use more energy?  What is the correct air pressure?

Are there any other causes?    I turned off the blades and it didn't
seem to make much difference and mowing where I had already mowed didn't
seem to affect it either.   It just seems to work harder to move the
tractor.   I did grease the front tires in the spring.