As far as driveability and fuel economy that I experienced on a 83 300SD:

1.valve adjustment....easier starting, better idle, better pick-up
2.cleaned banjo bolt...allows boost to properly adjust ALDA (fueling)...better acceleration, more power noticed in passing situations
3.bought boost regulator on e-bay-$15.00--cause it is too difficult to adjust the old spring pop-off valve on the turbo...better power (uhh, boost gauge checked pre-installation showed only 6 lbs boost....factory is about 13-14 lbs & I settled for 12 lbs boost). Reset ALDA for more fuel (about 3/4th turn richer).
4.Did purge to knock out chunks of carbon from cylinders , got bunches (musta been a coal bin in there somewhere--and this was after an Italian tune-up that consisted of hundreds of miles of 85-95 mph.
5.Change air filter...little improvement.

All this netted about a 6 second drop in 0-60 mph time. Well worth it in merging into Dallas traffic (most noticed change was clean banjo bolt).

SPARKY THE DIESEL is currently undergoing a make-over. Have pulled most of interior for SEM vinyl paint redo (pink-amino is being changed back to palamino). Pool noodles to the seats at this time also. Repainting is next after a minor bit of rust removal. Have planned H & R springs installation...need to keep up any and all momentium. An getting better wheels and tires will help that also. Wanna try rebuilt injectors also. Will propane fumigate the darn thing in an effort to get a little better fuel mileage (based on cost per mile--the only fair way to determine validity --with baseing fuel costs to a standard to account for $$ priceing variations).

Ultimate performance improvement....a new BlueTech engine, tranny, and computer (chipped)....prolly never happen, but I have hopes!

Regards

Run-em
1983 300SD- aka- SPARKY THE DIESEL