Not sounding like you know what you’re talking about

Not sounding like you know what you’re talking about Hey everyone , So I work in IT and I have to deal with customers in person and on the phone. Nine out of ten times I have the answers to their questions but the problem is when I feel a block coming i do what we all do I’m sure and substitute the word for another. This can sometimes make it seem like I’m not confident in the information I’m giving and it definitely negatively affects me both personally and professionally. It feels like such an uphill battle sometimes , and I’m just here to complain and get this stuff off my chest. Also I may seem rude on the phone sometimes because I can’t get certain greetings out or goodbyes. That definitely sucks. Anyone else deal with this?