There is a test sequence on the blower motor. The rattle from the suspension could be the bushings, but be sure the lower stiffening rods are properly tensioned. This is a part of the service that many forget. Also, the belt tensioner could be faulty, but I don't think that they are 500+labor, but the dealers could be higher than us.?.
You may want to get a GOOD indpendent to look at it for a second opinion.
1991 GMC Syclone
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