'99 Tahoe

I have a 99 Chevy Tahoe with 178M miles. At various points in the past few years I’ve spent major $s repairing/replacing things like the transmission, front end, a/c, plug wires, fuel pump, radiator, etc. The vehicle runs pretty well for it’s age and condition and I hope to drive it for a few more years. However, the problem that my mechanic(s) cannot pinpoint is this. The vehicle randomly (most of the time) at highway speed (>50 mph) tends to want to stall out, spit sputter while trying to maintain constant speed going uphill over a along incline. It just will not run normal in that situation unless I ease off the throttle. Don’t know if this is a fuel problem (but I’ve had all new injectors (spiders) replaced with new), an exhaust issue (fuel or air sensors), transmission overdrive issue and so on. The Check Engine light will come on sometimes and i have had the code read but it only comes up to a general default. I would really like some guidance. Otherwise, i guess I just live with the ol’ gal just the way she is. Thanks.

What was the code? It seems like even a generic code would help point to a possible solution. The code should be in the format of P1234.

But, as a WAG, when was the last time the fuel filter was replaced?