91 300e low gas mileage

[zxdent]

hi, I bought 300e 91 with 199k recently (after I crashed my beloved 300dt 87), and car runs good but gets barely 20 mpg even though I try to drive it very softly. Changed spark plugs (hd9 Bosh). The old ones were not bad either.
There is nothing to tune on the engine, but something does not work right.
How many mpg should good 300e 6 cyl. get if everything is OK?
Also I noticed the transmission does not want to shift right away but delays
for maybe 10-15 sec. when I take off first in the morning. Later in the day
works OK. Checked oil and it is OK.
Please reply if you have similar experience, or you know what I should check.
Thank you,
zxdent