LilRebel57

i have a 1995 s14 with an S13 sr20. Yesterday out of nowhere it wouldn't rev past 4500 RPM and then it slowly decreased how far it would rev until it died on me. I had it towed and in the morning it fired right up and had no issues revving all the way out. I then replaced the fuel pump today thinking the pump may have gone bad and it didn't fix it. After I tried a new battery thinking maybe it was because it wasn't getting enough voltage from the battery but that didn't work either. If I give it like 70-100% throttle it sputters but if I hold it at like 50% throttle it will rev all the way to 6500. But if I give it full throttle it only revs to 4500.. It's very weird and I have no clue what to do. Any help is very much appreciated