Great SWR, Poor Performance
It's possible to tune your SWR to an acceptable level (below 2.0), but still experience poor performance. If this occurs, there are two things that could be wrong.
Limited Radio Output Power
Though this is most likely NOT the problem, your radio could be defective and putting out little to no power. To check this, you’ll need to hook up a power meter to measure the output wattage. Most basic SWR meters should have a power setting that measures output power when the microphone of a radio is keyed. Hook up the meter and take a power reading of the radio. It should read at least 4 watts of output power. If you're getting substantially less than that -- or none at all -- you have a problem with your radio. However, the far more likely problem is that ...
You Need a Better Antenna
If your antenna tunes to an acceptable SWR level and you’re still experiencing poor performance, the problem is that you need a better antenna. Budget, window-mount or short antennas are convenient but have a reputation for providing sub-par performance. If you want better performance, you’ll need to invest in a higher quality and/or longer antenna.