Having strange shuttering issue's

[Dboy3er]

Hello Im new here I've had my 1991 318is for almost a year now

My M42 idles great drives amazing but lately I suddenly get no throttle response for a few seconds after driving for an hour or so I cuts power completly it will usually always do it in low rps 1st-3rd gear but has also done it in the high range a few times.  But it idles just fine

Any ideas ? Please help

Fuel pump &'Fuel Filter are New

[Dboy3er]

 I have also been getting bad gas mileage the old catalytic convertetr it had was hollow it now has one but some O2 sesor..