GM shows Three part numbers for the rad. support '89-'91. The Chevy & GMC are the same, the difference is in the headlamps (2-4 headlamp). To my knowledge, there are really only those Two, the third is most likely a minor difference (a hole or Two for a wiring clip/cooler, ect.). So your problem is likely just a bracket missing or broken. Hope this helps, Lorne