It really sounds like a derailleur adjustment problem to me.

Some questions:

Is is slipping on the front wheel or the rear cogs?

If rear - you say low gear - is this happening only on the lowest (largest) rear cog, or on others?

Was this a mail order bike?
If so, you will probably have to adjust both front and rear derailleurs. If you don't know how to do it, you'll have to learn or take it in somewhere.

My understanding is that Kent is mail order, and if so, I'd be willing to wager it's a simple adjustment issue.