There is really no single answer to your question. It depends on what the speaker wishes to say. "Past few years" does not on its own determine the tense of the sentence, notwithstanding the fact that it clearly describes something in the past. The past few years were terrible for me. The past few years have been terrible for me. The terribleness of the past few years will not dull my future. Technology advances during the past few years will greatly influence global Internet availability. Technology advances during the past few years have already greatly influenced Internet availability. Technology advances during the past few years are just now being fully understood by the general public. I could go on and on, but the point is, the phrase "past few years" does not determine tense of the sentence. Good luck with our sometimes confusing, but very flexible language!!

Past few years is a phrase.... it's a flexible phrase. It can be used in Simple past, past perfect, present continuous and etc

Present perfect (continuous). I've been doing a lot of fishing these past few years. I've lived here these past few years. The correct phrase is "these past few years". We never say "past few years" alone.

-we have made improvements over the last few years. -Did we follow the mass line over the past few years? -I am having a real hard time dealing with this for the past three years. -this movie was the bright spot of the last few years any correction is welcomed :-)