The use of the /sell command (/sell hand and /sell all) is really lagg creating and does create a peak in the CPU and RAM use. On small scale, it is not that bad, but on a bigger scale (say about 100+ people on your server) that sell full inventory's the server really does start to feel it and get affected in an negative way.
Get the command and code behind it get an improvement?

Closing due to inactivity. If this is still an issue, please open a new issue. (I'm not sure why you're selling kits that fill an inventory, though.)