Serious stuttering, new z owner needs help

[dmburke25]

Ok... So, When I purchased my 90' 300zx N/A it ran decent. Could tell it needed a little work. I took it to a specialist (awesome.org). The driveshaft replaced, new battery, upgraded intake, down pipe and catback. After that it seems the car just went down hill. It started to seem like it was running rough. Driving at minimal speeds the car would ride fine but as soon as I started to go faster (around 60+) the car would start stuttering violently and no matter how far i pressed in the gas peddle the car would just bog down as if it wasn't to stop and stall out. So my issue is, the "specialist" said my #6 injector was out, the tps connector needed to be replaces, I needed a new knock sensor, new o2 sensors, and spark plugs. Well Over 1k later i had all of them all replaced and the connectors cleaned and checked. I was driving home and it seemed to be running great but same thing started to go on once I got on the freeway. The stuttering and jerking is continuous once it starts no matter the speed. I mean it's harsh, my rpm jump up and down (weird) jump to 3 then 4 then drop down to 2 then up to 3 jerking the car hard. Can someone please help me. The "specialist" really are charging me an arm and a leg and obviously misdiagnosed the problem. HELP.