05 Chevy trailblazer 20mph why

I’ve replaced the starter, battery, injectors,
mass air flow sensor, detailed the throttle
body, and gutted the catalytic converter due
to its way cheaper and a very tight budget,
the only things left to change is the coil packs
and spark plugs. Before I changed the
injectors, mass air flow and gutted the
catalytic converter it had died on me twice at
red lights and was using fuel like crazy. Now
that all of that has been replaced it will only go
20 mph and then lose the pressure in the gas
and brake pedals I’m at a lose on what the
issue could be so I could definitely use some
help