Ken, What makes you think your current device is not up to the task? R/C systems are very slow IMHO relative to processors. Think on this, pulses for the car happen for 1-2msec each every 20 msec. so 2 pulses (drive & steering) will be max 4 msec. That leaves 16 msec for the uP to do whatever like measure distance and decide what to output next. At 4Mhz clock, thats 16000 ASM instructions! Not PBP instructions but still a whole lot!

So heres a couple of thoughts: Use pulseout for the signals to the car. No need for int or PWM. How about connecting 1 of the car signals from the receiver to your pic. Then just check to see if the pin went high, if so its time to send out commands. This way you can use the car receiver as a 20mSec clock.