I purchased a cheap kettle charcoal grill a few weeks ago, and I feel like it's not getting hot enough. I'm using a charcoal chimney which takes about 40 minutes to get the coals ashy. I've read it should only takes 15 minutes to light. Once I dump the charcoal into the grill it gets cold fast. When I first put my hand over it the grill is hot, and I can barely keep my hand over it for a few seconds. After closing the lid and letting the grill warm up for 5-10 minutes I can typically keep my hand over the coals much longer. I also never see any smoke coming from my grill after I initially light the chimney. I'm currently using briquettes as lump charcoal was even colder. The bottom and side vents are fully open, so there should be plenty of air flow in my grill.
It really sounds as if you're just getting the tail-end of the fuel left in the charcoal.. that you've let it burn too far in the chimney .. 40 minutes does sound like a long time .. the right time to start cooking on charcoal is when any self-sustained flames have gone down, and the surface appears grey-white in daylight.. if you fan it, there should be a clearly perceptible glow.
If you want to use your chimney, give the charcoal just enough time in there to propagate its own burn.. don't spread it too thin in the grill after transfer, and let it settle to a glow in the grill, not the chimney. That will also help the metalof the grill heat up.
Or, light the charcoal in the grill by fanning it gently, and later, not so gently, with whatever comes to hand, or an electric fan.