Ah, there is some hope. It is interrupting at least once. I had missed the test point signals that occurred after 25us. So now to find out why it only interrupts a single time.

Here's my latest code:

PLL_SETUP:
RCV_CLK_BIT = 0
TP_RCV_CLK = 0
TP_RCV_CLK = 1
TP_RCV_CLK = 0
TP_RCV_CLK = 1
TP_RCV_CLK = 0
'SET_25US_TIMEOUT: ' set timer0 for 25us timeout, 40MHz clock
T0CON = %00001000 ' Internal clock, no prescale, Timer0 off for now
TMR0H = $FF ' Timer0 low & high bytes set for 65286, 25us
TMR0L = $06
'
ASM
;MOVLW B'11000111'
MOVLW B'10001000' ; TMR0 on, 16-bit, no prescaler
MOVWF T0CON
BCF RCON,IPEN ; disable priority interrupts
BCF INTCON,TMR0IF ; clear TMR0IF
BSF INTCON,TMR0IE ; enable TMR0 interrupt
BSF INTCON,PEIE ; peripheral interrupts enabled
BSF INTCON,GIE ; global interrupts enabled
ENDASM
RETURN

ASM
pllInt
bsf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock

;btfsc _RCV_CLK_BIT ; if RCV_CLK_BIT is clr, set it and TP_RCV_CLK
;goto clr_RCV_CLK_BIT ; RCV_CLK_BIT is set, so clear it and TP_RCV_CLK
;bsf _RCV_CLK_BIT
;;bsf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
;goto continue
;clr_RCV_CLK_BIT
;bcf _RCV_CLK_BIT
;bcf _TP_RCV_CLK ; clear TP_RCV_CLK, LATF.7, test point for rcv clock
;continue
bcf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bsf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bcf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bsf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bcf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bsf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bcf _TP_RCV_CLK ; set TP_RCV_CLK, LATF.7, test point for rcv clock
bcf INTCON, TMR0IF ; clear TMR0 interrupt flag
RETFIE FAST
ENDASM