'06 Pete 387 N14 rpms

Hello, I bought an old truck to go out on my own in a few months. I was driving it home, bobtail and the pyro was being difficult. It was red lining every time it was going up hills or even when I shifted (10 speed eaton). What is the cruising rpms for this engine? I was holding it between 1300-1500 but it still was getting cranky whenever there was even the slightest grade. I'm worried if it does this bobtailing, wtf is it going to do when pulling something?
I don't know what the ratio is but I could hit 80 mph at 1500 rpms.

 

Thank you everyone for your response. I was wrong, it is an isx not an n14. I was bringing it home from the mechanic. Just got all fluids and filters changed.

 

That's lugging? I was taught to not take the engine over 1500. I did notice that it seemed to pull smoother when I took it higher and I couldn't downshift unless I kept it over 1000. But I had the pyro issue every time I took it too high.

 

No, my bad. It is an isx.