Im running chevy 250 with Clifford street cam, Head redone to Clifford specs valves , redone runners, cleaned up with studs installed.
stock piston and crank. Clifford intake no heat four barrel mounting plate with Holley 390 52 mains 8.5 power valve lighter secondary spring and stock size nozzles and 12 in oval air cleaner 2 in high
Clifford long tube headers Cliffords x pipe and magniflow 3 chamber exhaust 2.25 tube all the way duals. With modified chevy HEI big top distributor.
Dino around 200 hp and 265 torque I think if memory is correct at rear wheel. Trans is a stock t5 5 speed out of a s10 with a clutch matched from a v8 t5
stock rear end gears from stock 6 3 on the tree set up from 1977.
My truck runs decent not a rocket ship from the parts I have listed is there a piece to the puzzle Im missing or should revisit or look in to like rear end gear, weber carb single over Holley what air cleaner or size are u using
also running a big wide tire 295 45 20 not sure if big tire is robbing power it looks good. What's ur thoughts appreciated .

1977 chevy Stepside with inline 250

Yes sir

with big tires you're killing the gearing. Chevy loved there 308 gears. If that is what was stock. How Tall is that tire?

What rpm is it doing on the highway? And at what MPH? IE 2500 rpm at 60

30.5 diameter 11.5 wide

Don't have rpm gauge. Look s like I need one.

If you don't know the rear gear ratio, there is a code stamped into the axle tube. It will start with 3 letter and then have 4 or more #'s after that. Find it.

You may be able to see your trucks option list in the glove box or under the hood. It will tell you the ratio or the option code for the rear axle.

I pulled cover and counted 34 ring gear 10 pinion gear so I guess its a 3.40

I did some quick calculating with you .82 od ratio and looks like 70 MPH is about 2200 rpm. Not bad.
Looking at my dyno charts on this page https://www.12bolt.com/65279inline-cylinder-head-flow65279.html
The bolt in lump kit will give you a additional 10+ Ft Lbs TQ across the RPM range.
If using a mechanical fan, it can be changed out for a electric fan for greater efficiency of the engine.
Optimal timing can also help out.

Does head have to be removed to install lump kit.
Ive also had head work per Cliffords machinist bigger valves they sold.

Yes and the valves need to be removed at the very least one has to be out no matter what. But best to removed them all so the head can be cleaned properly once all the milling/cutting and grinding is finished. To remove the bolt boss that is in the intake port. The top of the head will need to be machined as well and tapped for the pipe plug that will need to be installed.