Step on gas and engine studders

Sounds like the accelerator linkage or kick down band of the transmission need adjustment.

Waste gate is sticking.

Couple of things....fuel filter could be pretty clogged....fuel pressure regulator is bad....
To make a better fix for you, can I get the info about your vehicle? Year/model/engine size?
Thank you.

I will suggest that you replace the fuel filter

did you also replace the inline fuel filter?

low speed activation of abs[will not set off code ] can also do brake studder without touching brake usually does it under 5 mph the problem is one of the sensors is dirty or has some corrosion on it ===chevy back in 2000 did a partial recall on the tahoe for the same problem the fix was to remove the sensor and clean it if the corrosion was to bad than sensor was replaced === the problem with no code is u dont know which sensor is causing problem u would need to remove both and check them

My 97 Legacy started to studder when stepping on the gas from a dead stop. It does not seem to studder at higher speeds. Do you thing the Fuel filter may need to be changed?

did you try using gas line antifreeze in it almost sounds like you have moisture in the gas

check head gasket look in radiator when cold,see if the water bubbles when cranking.

run the fault codes
check for problem MAF?VAF sensor and accelerator position sensor