Ping between Routers Issue

based In the topology below:
 I can ping from R4 all the way to R3 S1/1 interface but not to R3 interface S1/2.
I can ping from R5 to R3 interface S1/1 but cannot ping R2 S1/1

I know that I have configured Default Route, however I am not sure if that can be the issue.
I will post the Configuration of R5 and R3 now and if you need more information, please let me know.
Thank you.

 R5#sh run
Building configuration...

Current configuration : 1179 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R5
!
boot-start-marker
boot-end-marker
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
no ip domain lookup
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!
ip tcp synwait-time 5
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/2
 ip address 3.3.3.5 255.255.255.0
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 3.3.3.3
!
no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line aux 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line vty 0 4
 login
!
end

R5#
========================================

R3#sh run
Building configuration...

Current configuration : 1217 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
no ip domain lookup
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
!
ip tcp synwait-time 5
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial1/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 ip address 1.1.1.3 255.0.0.0
 serial restart-delay 0
!
interface Serial1/2
 ip address 3.3.3.3 255.255.255.0
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 1.1.1.2
ip route 0.0.0.0 0.0.0.0 3.3.3.5
!
no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line aux 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line vty 0 4
 login
!
end

R3#
============================

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