I looked on Livestrong.com and here is what it said.
"Karo syrup is a liquid sweetener made from dextrose, or glucose, and other corn starch sugars. You can buy Karo corn syrup in five versions: dark, light,
low-calorie "lite," brown sugar and pancake syrup. It also said that high fructose corn syrup was added to the light syrup at one time but do to all the public concern the use has been discontinued.
Karo does not recommend substituting other sugars for the corn syrup.
"It reduces the formation of sugar crystals in candy making; prevents ice crystals in frozen desserts; thickens relishes and enhances fruit flavor. In baking, corn syrup retains moisture and preserves freshness."
"The Colorado State University Extension offers a differing opinion: The school suggests that 1 cup granulated sugar added to 1/4 cup water -- or other liquid from your recipe -- is a suitable corn syrup substitute. A cup of honey is another alternative."
Here is the nutritional information on from Karo on the "lite" corn syrup. While I have not used this particular product I have substituted one for the other many times.
Since molasses is made from sugar cane I am not sure if there is such a thing as a sugar free version. About.com recommends the following as substitutes along with a note regarding flavor.
1 cup dark corn syrup, honey or maple syrup
3/4 cup firmly packed brown sugar
3/4 cup granulated sugar, plus 1/4 cup water
Note: These substitutions may alter the taste of your recipe a bit. If the molasses flavor is vital to the success of your recipe, try the brown sugar substitute. Since brown sugar is made from granulated sugar and molasses, it'll be the closest flavor match.
Would Splenda Brown Sugar blend work in the recipe? I'm not sure. I really try to stay away from artificial sugars but do understand the need for some to use them. Pecan pie is a very once in awhile treat in our home so I try t use the real thing--Karo Syrup. I may look for the lite version in the store.