I can't give you any RPM ranges, because my tach doesn't work...

Going downhill, I can get it up to like 86 AT the most, and uphill, around 65-70 or so. And that's at WOT.

It's a 7.3 N/A, and it's all stock as far as I know

 

It probably needs a timing bump and/or new injector pump and injectors for best performance... but those numbers seem reasonable for a non-turbo IDI. Before I got my turbo, I found that 70 was pushing things a bit.
That's why, for a big power bump, you want to find a used turbo kit, install it and turn the pump up a bit. Really makes a difference, especially at the higher revs.

 

My N/A will peg the speedo going uphill...though I have a proper y-pipe and cold air intake. Guess I can't remember how she used to drive when stock, lol.
I'd say you should be able to do the same on flat ground, even bone stock, assuming your engine is in good health.
Rob already covered the basics. Timing goes a long way with these engines, and I'd start there.

 

Hmmm, I'm guessing I could do that myself without taking it to a shop. I'll take a look at it tomorrow!

 

it all depends of a few things.
what size tires?
what gear ratio?
what trans?
has your speedometer been calibrated to tire size?
i used a GPS to make sure the speedometer is reading true speed. GPS says 76 when speedo needle is centered on 75
my 88 with C6 trans, 4.10 gears and 37 inch tires has a top speed of 82 MPH, and it takes 3 miles to go from 70 to 82 on flat ground.

 

My speedo is correct, I ran it by one of those radars and it was right. I have 3.55, and stock gears as far as I know. It's a E40D

 

that sounds about rite than.
remember, these trucks were made when the speed limit was 55 mph, and were designed for power, not speed.

 

Haha, I can tell, because of the red line on the speedo at 55

 

If you've got an E4OD, you *should* have 4.10 gearing... What RPM are you going at 60 MPH(in OD)? If it's in the 2100 range, you have 4.10. If it's in the 1700-ish range, you have 3.55s.

If you do have 4.10 gearing, you can swap in 3.55 gearing for a very good combo that gives you good efficiency on the highway going 60+MPH.

 

on the front driver side of the engine there is a large nut with two wires coming out of the middle of the nut.
unplug the plug, and remove the nut. this is the tach sensor.
clean it off real good and reinstall it. the tach may start working again.
do not drive the truck too much until you get the tach working properly, the E4od trans needs tach signal to work.
my bet is you are not shifting into overdrive.

 

That would explain why my overdrive light is flashing! It all makes sense. I just finished up a 4 hour oil change so that'll have to wait until tomorrow morning.

 

My van with 3.55s and a C6 maxes out at 85, so yours likely isn't shifting into od.

 

Makes sense.

 

Get your tach sensor working yet?

 

Haha, no. One day I went out in the morning and started the truck up and the tach worked for that entire drive. No OD light. Next time I went out, it didn't work... Strange.