Not sure about the 350 but I do believe thats what I run at 60 with my 4.3.
But I am standard tranny and I rarely run 5th gear anymore because she
doesn't like it.    How many miles do yo have on your truck?

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1,900 to 2,200 I would say is the average.

2,600 is totally ridiculous. 4.10 gears and a three speed would probably
run slower. check that tach again.

HDS

To run 2,600 @ 60 mph with 3.42 gears you would need 24" tires....
http://www.drivetrainsuperstores.com/gear_ratio_chart.asp
click the link, know your tire size and read the chart,
you want to be in the pink area of the graph.

A little high in my opinion.  Is your torque converter locking up???  When
driving down the road lightly press on the brake when you have you other
foot on the gas.  You should feel the converter unlock and the rpm will kick
up ~500rpms.  I have a 4.10 rear on truck tires (stock to the 3/4 ton
burban) and run about 2100-2200 at 60mph. I bet your converter is not
locking up.  You probably have a 3.21 or 3.73 rear if you look at the
options sticker (glove box or some place similar it should tell you) or you
can take you vin into your local friendly dealer and they can tell you.

good luck,
mark

 I`m almost positive you have either 3.42 or 3.73 gears.
Are you running in drive,or overdrive?

Did you remember to set the tach for V-8 application?

                           ********************
       

 That is to high if yor running in od.
What brand of tach are you using?

When I hooked a scope to the truck and revved up the engine, the tach showed
2600 and the scope showed 2000. The tach needle also jumps around abit.
I put the tach in different vehicle and it operated perfectly.
Do I maybe have a coil problem in my truck? There is a slight miss in the
engine when it idles.

Alex