Were in Lincoln. Where are you located in Nebraska?
What others have said is right on the money. There is a test kit to pressure test that furnace which will tell you if the heat exchanger is bad. If so it needs to be replaced. Lennox has a program that will help you save alot of cash on a new furnace. If it is not cracked then it needs to be repaired. It was one of the most efficient furnaces on the market and still is today. Are they telling you that it needs replaced because they don't know how to repair it? Fing a Lennox dealer that knows how to repair it as most repairs on a Pulse are simple. I don't know what would need to be torn apart to figure it out.
That being said, it dosn't really matter what brand of equipment you purchase but who installs it. Lennox has heat pumps that are built really well but if not installed properly they will fail. Search for a contractor that knows what they are doing and you should not have a problem.
On a side note I don't know of a Lennox system that has a lifetime compressor warranty.