when to shift into overdrive? on a 93 4.3 auto 4x4

hi all..........
i was wondering when you guys with trucks of my year and config...
shift into overdrive.
i usually shift to o/d at about 60 ...but when i go up hills the engine seams to strain untill its shifts down and revs up the engine.
though when i stay in drive at the same speeds on hills i barley need to step on teh gas to get up hills.
when i drive at highway speeds i like it much better...as the engine obviously feels stronger being in 3rd only.
also there doesnt seem to be any gear drag slowing the truck down
when in drive at highway speeds in drive.
i have a friend with a 97 s10 ...and if you leave that truck in drive at even 60 ..you can feel the low gear drag right away when you take your foot of the gas....unlike my 93.
i know that by being in drive it wont go into o/d but whats the recomended speed to shift into o/d....i dont have a manual so i cant look it up......some input would be appreciated.

OD all the time, everywhere - for best gas mileage. I only take it out of OD when hauling loads of cargo, or climbing steep terrain at highway speeds. (There are a ton of hills out here in the Ozarks) Under light to moderate acceleration, proper OD shift will occur at 45 MPH. Heavy throttle like when merging into traffic at highway speeds, it will be delayed until 55 to 65 MPh depending on the circumstances. It will kick down out of overdrive into "passing gear" when pressed down more than 3/4 throttle~floor when moving at most highway speeds.

It's not a power gear, no - but rather it allows the engine to run at much lower revolutions to save gas, wear and tear on the truck. Driving in OD also helps the tranny keep itself running cooler. Google up info on the GM 4L60E overdrive tranny to get all the info on it.

I'm with wolfox...Even in the manual it says to leave it in OD as normal driving and down shift for loads.

kool...i have been driving mainly in o/d.
one more question....if i may.
if im driving on the highway at like 60-65 is it safe to put it in drive if im goin up a kinda steep hill?
you guys recomend that at those speeds?

It will rev higher is all, you get the same effect pressing down on the gas till it shifts.

thanks for the info....much appreciated