Engine hiccup at higher speeds when accelerating. How should I troubleshoot?

[CorMun]

'99 Yukon, 56k miles. I'm new to these rigs, so go easy on me. It's been sitting in a garage for many years before I bought it. Starts fine, shifts fine. At cruising speeds (around 60-70 mph) when I hit the accelerator, it will stutter once or twice. Doesn't seem to occur at lower gears or lower speeds. Overall acceleration seems sluggish, but again, I'm new to these engines and 4 sp transmissions.

I just bought it and plan on replacing everything that I'm capable of. Where do you think I should start?

 

[2016Dom]

Start with plug, wires, cap and rotor, clean the throttle body.

 

[Fless]

If you have history on it, see what's been done recently. If regular maintenance hasn't happened, start with what @2016Dom noted, except that it probably has the spider injector fuel system.

As to the specific issue, I'd probably start by 1) testing the fuel pressure and 2) connecting a fuel pressure gauge to the windshield to monitor what it does when the issue happens. If nothing else it will rule out that cause. Fuel pressure test kits can be rented at most auto parts stores.

 

[Eman85]

You can test fuel pressure and go over the ignition system. If it truly has 56k and has been sitting I'd start with a fuel sample and a new fuel filter then a fuel pressure test.
I came back to edit this. Before replacing parts it's better to have a direction with diagnosis. Replacement parts today are not always as good as the 25yo part you take off and many times you're installing a problem instead of fixing one.

 

[exp500]

Another Diagnostics first recommend! Scan for codes, then long test drive with live data displayed. Can do fuel pressure test at same time.
Use ONLY Delco/Delphi or United DCR820X cap/roror. NGK or Delco plugs