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The 3750X can easily provide 1 gig throughput on a gig port. The likely issue is, you're sending bursts of more than 1 gig to a gig port, and there's insufficient buffing to handle those bursts, so you see drops.
To decrease the drops, you'll need to better control bursting and/or improve buffer management.
For example, if your hosts using the iSCSI device are on gig ports, you might try running them at 100 Mbps. (Unfortunately, this alone, besides "slowing" them, may result in egress drops on their ports.)
If your iSCSI devices is not already on a "uplink" port, move it to one. (On the 3750s, each bank of 24 copper ports has 2 MB of buffers, as also do the switch's "uplink" ports.)
On a 3750, I've found you can often much, much reduced egress drops (NB: actually for iSCSI port, too) by enabling QoS, and configuring buffers to be in the common pool and use it dynamically (rather than reserving buffers to interfaces).
