Unusual Miss

Please help!
OK folks, here's my problem.
First of all, I have a 77 3.0 in my 76 Targa.
Everything has been fine until the other evening. While entering one of our local highways and accelerating up to 3000 rpm all was fine, however, between 3000 and 4000 rpm, the engine ran terrible. It felt as if the engine just could not go any further. It spit and sputtered up to 4000. Once past 4000 rpm, all was fine again. This happened through each shift. And this continues to happen. I have just come in from checking the points, dwell and timing, which were all ok. Also checked vacuum hoses which seemed fine. Any suggestions to point me the right direction would be greatly appreciated.

Steve Anderson
76 Targa

Have you changed your fuel filter, lately?

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Warren Hall
1973 911S Targa

The fuel filter was change about a year ago. I wasn't sure how often this was needed. I do have a spare and I was thinking of changing it out to see if that could be the problem. Thanks Warren.