Stumbling during acceleration

1999 Tacoma 2.7l 5 speed 4x4 205,000 miles. Truck idles at around 700 rpm's and is smooth. Runs good driving around and shifting at low rpm's but if you take her above 3500 it seems to have a hesitation. It's not always but it is happening more often lately. I have replaced both coil packs, wires, plugs and fuel filter. I plan on pulling the throttle body and cleaning it good along with the IAC and TPS. Just wondering if anyone has had any symptoms like this and what fixed it. I hate to just throw money and parts at it but it is getting annoying. Could O2 sensors or fuel pump heading south be the cause? Thanks for any suggestions y'all have...it is appreciated.