I find I can't make eye contact with people when I am talking to them.. it's hard to focus on what I'm saying if I'm looking them straight in the eyes.
People of all types will usually break eye contact when they try to recall something. There's even a learning style test that relies on this, suggesting whether someone looks up, down or to the side when answering a question about yesterday's lunch indicates a visual, auditory or kinesthetic learning style respectively.
Also, it's been shown that
children who avoid eye contact while considering their responses to questions are more likely to answer correctly than children who maintain eye contact.
These moments happen more often for Ti/Ne types as they absorb the new information from the conversation and assimilate it with existing ideas.
It's interesting you have this problem
while talking. Are you trying too hard to act extravert, thinking and speaking at the same time?
Most chit chat requires no thought at all - there's no need to think about what you're saying because it's just meaningless noise.
In deeper conversations it's okay to take them time to think before you speak. Once your answer is composed it's easier to make eye contact while you're delivering it.
This can appear rude - glancing up looks like an eyeroll, glancing aside looks like distraction - so developing an alternate "thinking face" is a good idea. Saying "um" while you think is inelegant, but it does the trick. A visual "um" could be closed eyes or a big breath. Some company may even let you get away with "stand by, I'm processing your request."
However, I've found that I do look people in the eye when they're talking to me.
This will earn you forgiveness from those who took offense when you broke eye contact to think.

I have some trouble with this now but it has nothing to do with type. I'm going deaf. If there's a lot of background noise I have to look at someone's mouth when they speak.
Also: I know most people don't make eye contact if they're frightened or lying
This is a non sequitur derived from the western cultural norm of making eye contact to signal openness. In practice it's almost never true.
Liars are very good at looking people in the eye, using the cultural norm to support their deceit. The frightened will frequently stare, either assessing their danger or signalling aggression.
People from many islamic, asian and australian aboriginal cultures avoid eye contact as a sign of respect. Western women, in situations where eye contact may signal openness to a sexual advance, look away to avoid flirting.
And, as above, people break eye contact when they're thinking. Some people will infer deceit from thoughtfulness but personally I'm happy to let this happen - I take it as a sign they're thoughtless and deceitful themselves.