i bought a used 1999 tacoma 3.4 v6 with 300,000 miles and the previous owner did not keep up with maintenance what parts should i replace first to get truck to run better

What is your question?

My check engine light is on. My truck has no power going up a small hill. My temp gauge is always on low even after truck warmed up

What makes this problem better or worse?

The problem is neither getting better or worse

How long has your 1999 Toyota Tacoma had this problem?

almost a year