Ubuntu 11.04 Natty upgrade underclocks and disables CPU scaling on Thinkpad T40p

I have an IBM Thinkpad T40p with a Pentium M 755 2.0 GHz CPU. After upgrading to Ubuntu 11.04 from 10.10 the CPU is incorrectly underclocked to 598 MHz and cannot be adjusted, manually or automatically. When I boot off the old 10.10 live CD, CPU scaling and all the governors work again perfectly. The 11.04 live CD however has the same problem.

I've tried loading every possible scaling module I could think of (acpi-cpufreq, speedstep-centrino, p4-clockmod, cpufreq_ondemand) and tried multiple scaling daemons and programs with no luck at all. I'm stuck at what to try next.

The Gnome Panel CPU Scaling monitor says "CPU frequency scaling unsupported" and here is the output of various commands:

$ cpufreq-info
cpufrequtils 007: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to <email address hidden>, please.
analyzing CPU 0:
  no or unknown cpufreq driver is active on this CPU
  maximum transition latency: 0.00 ms.

$ sudo /etc/init.d/cpufrequtils start
 * CPUFreq Utilities: Setting ondemand CPUFreq governor...
 * disabled, governor not available...

$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 2.00GHz
stepping : 8
cpu MHz : 597.949
cache size : 2048 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 ss tm pbe nx up bts est tm2
bogomips : 1195.89
clflush size : 64
cache_alignment : 64
address sizes : 32 bits physical, 32 bits virtual
power management:

$ ls -h /sys/devices/system/cpu
cpu0 cpufreq cpuidle kernel_max offline online possible present probe release

$ ls -h /sys/devices/system/cpu/cpu0
cpuidle crash_notes topology

$ ls -lh /sys/devices/system/cpu/cpufreq
total 0

$ ls -h /sys/devices/system/cpu/cpuidle
current_driver current_governor_ro

$ cat /sys/devices/system/cpu/cpuidle/*
acpi_idle
menu

$ dmesg | grep -i cpu
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] PAT not supported by CPU.
[ 0.000000] SMP: Allowing 1 CPUs, 0 hotplug CPUs
[ 0.000000] setup_percpu: NR_CPUS:8 nr_cpumask_bits:8 nr_cpu_ids:1 nr_node_ids:1
[ 0.000000] PERCPU: Embedded 13 pages/cpu @f5800000 s28800 r0 d24448 u4194304
[ 0.000000] pcpu-alloc: s28800 r0 d24448 u4194304 alloc=1*4194304
[ 0.000000] pcpu-alloc: [0] 0
[ 0.000000] Initializing CPU#0
[ 0.000000] SLUB: Genslabs=15, HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[ 0.000000] RCU-based detection of stalled CPUs is disabled.
[ 0.000000] CPU 0 irqstacks, hard=f5406000 soft=f5408000
[ 0.008754] Initializing cgroup subsys cpuacct
[ 0.008939] mce: CPU supports 5 MCE banks
[ 0.060134] weird, boot CPU (#0) not listed by the BIOS.
[ 0.064798] Brought up 1 CPUs
[ 0.216353] Switched to NOHz mode on CPU #0
[ 0.220886] cpufreq-nforce2: No nForce2 chipset.
[ 0.326754] ACPI: acpi_idle registered with cpuidle
[ 0.605330] cpuidle: using governor ladder
[ 0.605536] cpuidle: using governor menu

$ uname -a
Linux dep 2.6.38-9-generic #43-Ubuntu SMP Thu Apr 28 15:25:15 UTC 2011 i686 i686 i386 GNU/Linux

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=11.04
DISTRIB_CODENAME=natty
DISTRIB_DESCRIPTION="Ubuntu 11.04"