Well, I think I discovered the issue. I tried running my program on a newer computer on QB64 version 3.6.0 instead of version 2.0.2 on the older machine and, voila, no more sluggishness after the warp sub. Here's the sub that was causing issues before . . .
SUB warpTravel () ' *** WARP TRAVEL EXECUTABLE LOOP ***
DIM AS INTEGER speed, warp
DIM i AS STRING
DIM warpSound AS LONG
DIM back2SubSound AS LONG
speed = 15: warp = 4:
warpSound = _SNDOPEN("going.wav")
IF warpSound = 0 THEN SOUND 120, 1 ELSE _SNDLOOP warpSound
DO UNTIL i = "b" ' escape from warpTravel and back to sublight by hitting back ("b") button - for now
i = INKEY$
CLS
_LIMIT speed
moveFarStars: drawFarStars '
moveMidStars: drawMidStars '
moveNearStars: drawNearStars '
drawViewScreen
_DISPLAY ' *** TEMP USER INPUT ***
IF i = "p" THEN WHILE INKEY$ = "": WEND ' pause
IF i = "f" AND warp < 8 THEN speed = speed + 3: SOUND 650, .8: warp = warp + 1 ' faster
IF i = "s" AND warp > 0 THEN speed = speed - 1: SOUND 960, .5: warp = warp - 1 ' slower
IF i = CHR$(27) THEN SYSTEM
LOOP ' warp value to be used for displaying speed...
_SNDCLOSE warpSound
back2SubSound = _SNDOPEN("back2SubLight.wav")
IF back2SubSound = 0 THEN SOUND 100, 1 ELSE _SNDPLAY back2SubSound '
_AUTODISPLAY ' needed for speedy lightening effect
lightning
_SNDCLOSE back2SubSound
END SUB ' *** END WARP TRAVEL EXE LOOP ***
SUB warpTravel () ' *** WARP TRAVEL EXECUTABLE LOOP ***
DIM AS INTEGER speed, warp
DIM i AS STRING
DIM warpSound AS LONG
DIM back2SubSound AS LONG
speed = 15: warp = 4:
warpSound = _SNDOPEN("going.wav")
IF warpSound = 0 THEN SOUND 120, 1 ELSE _SNDLOOP warpSound
DO UNTIL i = "b" ' escape from warpTravel and back to sublight by hitting back ("b") button - for now
i = INKEY$
CLS
_LIMIT speed
moveFarStars: drawFarStars '
moveMidStars: drawMidStars '
moveNearStars: drawNearStars '
drawViewScreen
_DISPLAY ' *** TEMP USER INPUT ***
IF i = "p" THEN WHILE INKEY$ = "": WEND ' pause
IF i = "f" AND warp < 8 THEN speed = speed + 3: SOUND 650, .8: warp = warp + 1 ' faster
IF i = "s" AND warp > 0 THEN speed = speed - 1: SOUND 960, .5: warp = warp - 1 ' slower
IF i = CHR$(27) THEN SYSTEM
LOOP ' warp value to be used for displaying speed...
_SNDCLOSE warpSound
back2SubSound = _SNDOPEN("back2SubLight.wav")
IF back2SubSound = 0 THEN SOUND 100, 1 ELSE _SNDPLAY back2SubSound '
_AUTODISPLAY ' needed for speedy lightening effect
lightning
_SNDCLOSE back2SubSound
END SUB ' *** END WARP TRAVEL EXE LOOP ***