Matt Slick has again (The Bible Thumping Wingnut, Episode 61, around 30 minutes into the episode) erred on the topic of textual criticism.
Unfortunately, Mr. Slick seems to be confused about the transmission of the New Testament compared to the translation of the Old Testament. His comment about adding up numbers seems to be based on something Mr. Slick has heard about the process used by the Masoretes (and it doesn't even appear to be accurate regarding their process). It does not describe the Christian process, especially not in the early Christian period. Early Christian textual transmission was, as far as we know, not done by professional scribes and did not include letter-counting techniques (such as those later used by the Masoretes) to ensure the reliability of the copies. These facts don't undermine the reliability of the New Testament text, but making errors in this area may undermine the other valid points that Mr. Slick is trying to offer.
Additionally, Mr. Slick repeated the same error regarding how textual variants are counted (which we already corrected here).
It's great that Mr. Slick is going to be debating a Muslim on the divinity of Jesus soon, but it seems likely that these issues of textual transmission will crop up in apologetics with Muslims (as they frequently do), and it would be good for one of Mr. Slick's friends to help get him straight on these issues before then.
*** Updated 4/13/2015
By the way, Mr. Slick should probably update his own web pages once he realizes his mistake. This same repeated error about how to count variants appears on at least the following pages of carm.org :
That same page also claims "Furthermore, the New Testament is approximately 99.5% textually pure. This means that of all the manuscripts in existence they agree completely 99.5% of the time." That's also not the case.
This page claims "The copies are so accurate that all of the biblical documents are 98.5% textually pure." Even if Mr. Slick decides he has some insight into textual transmission, he should presumably harmonize his own pages.
This page also claims (similar to Mr. Slick's comments on the show): "Similarly, the Greek writers of the New Testament would copy the biblical manuscripts. By default, every letter also has a numeric value. When the copies were done, the copyists would add up the numeric values of the words copied and compare them to the original copy. If there was an error, the copy was destroyed and a new one was begun. This was done with both the Hebrew and Greek writings of the Bible. Therefore, the Bible was copied with extreme care." That's not an accurate depiction of the New Testament transmission. It seems to be taken from some information regarding the extreme care the Masoretes took in copying the Old Testament, but even then it's not quite right.
The page also mentions the accuracy of the Isaiah scroll in the Dead Sea scrolls compared to the Masoretic text. It's true that the texts were very close. Not all the scrolls share that same closeness, however, especially in Jeremiah. So, it might be good to provide some additional information and caveats regarding the reliability of the Masoretic textual transmission.