Did the Shaver company or other supplier provide or recommend the 007, size of manifold, underground lines, etc.? If so, get back in touch with Shaver/supplier and see what they have to say.
With a temperature difference of 120 supply and 60 return, that shows that your floor temp is 60 or less, and I agree that it may take a long time, even up to several days, to heat that floor up to your desired temperature. Give the system time to get up to speed.
I don't have enough info to conclude that the 007 is off the curve (under-sized) in your application, but it could be. To determine that I'm going to assume that the 007 is the supply circulator from the boiler to the manifold. What is the total round-trip distance of the 1" pex between the boiler and the manifold? With that info it would be possible to determine the approximate pump head between the boiler and the manifold and then the pump head of the in-floor pex could be added in to determine how much water the 007 can supply to the floor. You would want to be able to supply 0.4-0.5 gpm for each loop, about 1.6-2.0 gpm total.
If I assume the boiler is 200' from the garage, or 400' round trip distance of 1" pex, then the pump head to the manifold at this distance and at 2 gpm is about 3.3 feet. The pump head at 0.5 gpm in 300' of pex is about 3.6 feet. Total pump head then is about 6.9 feet, and at this pump head the 007 can supply more than 2 gpm to the floor, which should be sufficient. Others can correct me if my calculations are in error.