I believe at 40 MPH you will be in third for the most part. At low speed with light load I try to keep the rpm's below 2,000. In Delaware it not a problem but here in Washington theres lot of hills. For some reason I get better mileage and performance here in Washington. Must be all the trips here are longer and fuel quarity is better.

_________________
2006 Black Jeep Liberty CRD Limited
K&N, Samco Hoses, Michelin 245/70-16 LTX A/T2, Fumoto F-102, V-Force Muffler, Mopar, Hitch, Trailer Wiring, Skid Plates, Slush Mats, Rear Shelf, Predator Stage 1, Transgo, ORM & CodeReader, Facet 40109 Pump
"IT'S A DIESEL THING, YOU WOULDN'T UNDERSTAND"
Certified Services Auto & Truck Repair

Right at lockup at 50mph would be the most fuel efficient. You really can't bog an unloaded diesel at reasonable RPMs (anything over 1200 RPM) but our rigs will never lockup at that speed anyway.

_________________
Manure green 2005 CRD sport4x4, GDE Hot tune, Cat Gut, OE skids, Draw tight hitch, Duramax lift pump, 160K on multiple varieties of fuel, XM radio, Escort live with Redline, fog light mod, GPS, Icom IC7000 all band radio call sign KC9QPF, Grabber AT2s on Soft 8s, FIA grill blanket.

ok sorry but i meant not about the 5 speed auto

im picking gears and manual trans that will work best at the most used speeds i drive 30 50 and rarely 70
i live in the sticks

i guess its more to find out if 1400-1600would be too low to to do light cruse at say 50MPH or if i should drop a gear to get the rpms up

just did the #s on a combo
nv3500hd NV242 and 3.55 rear got me
30MPH 3rd gear at 1605 rpm
50 mph 5th gear at 1404rpm
70mph 5th gear 1966rpm and 4th gear (tow ) 2693rpm
to me this looks liek a great combo but feedback would be great

_________________
planning a CRD into a dodge dakota (short bed std.cab)
5-6 speed 2.8l crd 4x4
i would just get a jeep but i need a truck bed