Couple issues

When driving, have to hit around 75mph (3400 rpm) before trans will shift from 3rd to 4th on its own (if i let off the gas it will shift). but once its in 4th, really not alot of power and speed will slowly decline. if i give it more gas, drops into 3rd again.

that normal? if not, what can i look at.

since its not near redline, not too worried about engine revs, but concerned.

I've been told that 3rd is designed to accel on the freeway.

I wouldn't worry about it personally. Do you have bigger tires and stock gears?

31/3.55 thought about 4.10, but one of those "later" things

I wouldn't worry about it too much, same thing happened on my 96 with bald 32s and 3.55s. With newish 33s 4th is basically useless. Your altitude probably isn't helping you either.

Don't worry about redline either, I did about 5-700 miles over the last 2 months in the 96 in second gear, on the highway, at 80mph, with a trailer. Same 33s and 3.55s. I was revving the engine anywhere from 4500 to 5200 (not sure how I got it past the rev limiter, but I did) for literally hours straight. Still works fine, oil pressure is the same as before, temp never went above 210.