Surging sputtering issue

Hello and welcome to 2CarPros. Being a 1995 you cannot easily scan it for codes, however I would suspect a faulty coolant temperature sensor or the wiring to it being it isn't a constant problem. Your vehicle uses two sensors, one goes to the ECM and the other to the gauge in the dash.
GM # 15326386 is the ECM sensor. It screws into the intake manifold next to the thermostat housing. A trick to changing it out without draining the coolant is to have a cold engine. Start removing the sensor until it is almost fully out. Now squeeze the top radiator hose hard. Release it and as soon as you do remove the sensor and screw the new one in, if needed a helper on the hose can make it much easier. Squeezing then releasing the hose will create a small vacuum inside the engine for a couple seconds, that is usually enough time to swap the sensor and only get a tiny amount of coolant out of the system.

You can test the sensor first if you have a multi-meter. Simply check it's resistance using the table I posted. However, you would need it to be acting up while this happens to be sure it's the part that's failing.

Another option would be to find a shop with an older scan tool that can read the data from the PCM and see what it shows while it is acting up. However that could take a while unless it always acts up.

I would also look at the connector real close, corrosion or damage can cause a lot of problems, many times more than failed parts.

I would check the wiring to the sensor. Being it was broke off the internal pins may not be making good contact and causing faulty readings.
The other sensor is for the dash gauge, if it is reading OK, the sensor is OK.
The exhaust leak can cause the O2 sensor on that bank to read a lean condition and add more fuel. As well.
We always like videos.

What other modifications are on the truck? It would have only had one O2 sensor. Plus a MAP, throttle position and coolant temperature. Does it idle okay?

Hello,

It looks like the TPS sensor is not working right but to be sure lets run the codes. this guide will help us:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Please run down this guide and report back.

Did this all start after the tune up? Or was this the reason for the tune up and it didn't change? What did you do for a tune up?

I was going to say coolant sensor but you did that. Did you manage to run the codes?

An O2 sensor could cause problems, but usually that would occur all the time not just at a part throttle situation, however it would depend on what it was actually doing. As the issue started after the tune up, I would just go over what you did, just to be sure that a connector pin didn't get bent or another item like a vacuum line or wire didn't get knocked loose while you were working. BTDT before.