a slow PS throughput can be caused by many issues, and most of them are NOT due to core network capacity.
First of all, you need to ensure that you have enough capacity on:
Air (radio) interface : PDCH capacity
Abis interface : packet abis ts capacity
Ater PS interface : packet ater capacity
once you are cleared on capacity, you can have a look at radio quality (coding scheme, retransmission)
50 packets lost, over how many packets ?
how do you count lost packets -> based on EGPRS ACK/NACK messages ? In such case, keep in mind that EGPRS is based on a typical threshold of 10% of retransmissions. Packets cannot be “lost” (afaik), they are only being retransmitted, except in case of real time.