Without Stack Cable that can accommodate 32 Gbps and no more Gig Ports available.
Cisco Catalyst 3750 Fast Ethernet Ports can be aggregated to be a trunk and to have n x 100 Mbps capacity.
“n” is the number of Fast Ethernet, the technology is called Port-Channel.

If you have existing trunk with Fast Ethernet, here the trick to migrate [configuration applied to both switches] :

A. Port Channel
1. Config Port-Channel “x”
x is what ever number
2. Set Port-Channel to be trunk
3. Set Port-Channel trunk type

B. FastEthernet
1. Config Fast Ethernet as Trunk also Trunk Type.
2. Config Fast Ethernet to be included in channel-group 1
Channel-Group 1 associate with Port-Channel 1
3. Don’t forget the mode channel-group is on [avoiding looping traffic ?]

If All done both switches,
C. Migration
1. Plug the Cross Cable in between ports
2. Immediately unplug the existing trunk [may be on fast1/0/48 for e.g]
Both action should be done at the same time, unless the switch stop to work nope sure this is a looping symptom or not.
3. Check the link in between by ping, trace, show interface etc.
4. If all running good, set you existing trunk to be included on channel-group x also do not forget the trunk encapsulation type.
5. You’ll now have 3 x 100 Mbps
6. Your traffic is not load shared……

D. Load Balancing
1. Config “port-channel load-balance dst-ip” [my choice]
2. Check the traffic load on trunk ports, it should be shared now.

Issue : still not balanced dan shared 100% the same volume on each of trunk interface.

====================================
port-channel load-balance dst-ip

interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk

interface FastEthernet1/0/1
switchport trunk encapsulation dot1q
switchport mode trunk
speed 100
duplex full
channel-group 1 mode on
!
interface FastEthernet1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
speed 100
duplex full
channel-group 1 mode on
=====================================

a. rahman isnaini r.sutan