The WalMart CC is GEMB, and I believe their CLI policy is pretty standard for everyone (read: stingy).
Apparently you have to generate at least 4 statements by leaving a balance on your account. After that, you can request CLI, but it is typically in the $200 range.
However, I was given an auto-CLI on my Sams Club Discover card (also issued by GEMB) from $4200 to $5200 the first month I had it. I did have a substantial improvement in my TU score that month though. I was approved at 642 and went up to 680.